MEMORANDUM
Defendants were charged,1 singly or in groups, in a sixteen-count information with one count of conspiracy, 18 U.S.C. § 371; five counts of attempting to persuade, entice, or coerce another to participate in interstate travel for the purpose of prostitution, 18 U.S.C. § 2422(a); four counts of successful persuasion, enticement, or coercion, 18 U.S.C. § 2422(a); three counts of transporting a minor in interstate commerce for the purpose of prostitution, 18 U.S.C. § 2423(a); two counts of transporting a person in interstate commerce for the purpose of prostitution, 18 U.S.C. § 2421; and one count of violating the Travel Act, 18 U.S.C. § 1952.2 The prosecution requested a Pinkerton instruction,3 which was given. The jury convicted Defendants on all counts.
First, we address the arguments that apply to all four Defendants. Second, we respond to the individual challenges to Defendants’ respective convictions. Third, we turn to the alleged sentencing errors.
A. Common Issues
1. Conspiracy
Defendants challenged the sufficiency of the evidence underlying their conspiracy conviction. Reviewing for plain error, we conclude that the conviction must be reversed because the jury could [754]*754have convicted on a legally inadequate ground. United States v. Fuchs, 218 F.3d 957, 961 (9th Cir.2000).
“Under 18 U.S.C. § 371, a single charge of conspiracy can have multiple objects, but each object alleged must constitute a federal offense.” United States v. Manarite, 44 F.3d 1407, 1414 & n. 7 (9th Cir. 1995). “[A] federal conspiracy conviction could not be upheld when non-federal offenses as well as federal offenses were submitted to the jury as objects of the conspiracy, and it was impossible to determine on which basis the jury convicted.” United States v. Croft, 124 F.3d 1109, 1115 (9th Cir.1997). In fact, a conspiracy conviction is “doomfed]” if the indictment alleges both legally sufficient and legally insufficient objects and there is “no way to know which objects the jury relied on in its decision to convict [the defendants] of conspiracy.” Manarite, 44 F.3d at 1413-14.
That is exactly what happened here. The information charged that Defendants conspired to violate three federal statutes. However, it then listed the conspiracy’s four “objects and purposes.” In supplemental briefing, which we requested, the government conceded-and we agree-that object number three, “[t]o obtain the proceeds of prostitution from females the defendants had recruited to work as prostitutes,” is not a federal offense.
The jury returned general verdict forms. We cannot determine which “object” of the conspiracy the jury relied on in reaching its verdict. Because the jury could have relied on object number three, the conspiracy conviction is legally unsupportable. See Yates v. United States, 354 U.S. 298, 312, 77 S.Ct. 1064, 1 L.Ed.2d 1356 (1957) (stating that “we think the proper rule to be applied is that which requires a verdict to be set aside in cases where the verdict is supportable on one ground, but not on another, and it is impossible to tell which ground the jury selected”), overruled on other grounds by Burks v. United States, 437 U.S. 1, 98 S.Ct. 2141, 57 L.Ed.2d 1 (1978).
Finding an error does not end our inquiry. Defendants did not object to this error at trial, nor did they argue it in their briefs to this court. Therefore, we can reverse only if this mistake constituted “plain error.” See United States v. Portillo-Mendoza, 273 F.3d 1224, 1227 (9th Cir. 2001) (defining plain error).
We already have explained that submitting a legally unsupportable theory to the jury was error. We conclude that the error was plain. The law in this area was settled at the time of trial by established Supreme Court precedent. Yates, 354 U.S. at 312, 77 S.Ct. 1064; Fuchs, 218 F.3d at 962 & n. 1. Further, the error prejudiced Defendants’ substantial rights because it appears to have affected the outcome of the proceedings, which relied heavily on Defendants’ concerted activities within Montana. See United States v. Olano, 62 F.3d 1180, 1188 (9th Cir.1995) (stating standard). Finally, we hold that the real possibility that Defendants were convicted for acts that are not federal crimes is grounds for us to exercise our discretion to reverse for plain error. See id. at 1187.
Because the conspiracy conviction may have rested on a legally insufficient ground, we reverse the conviction of all Defendants on count one. We next reach the question of the sufficiency of the evidence on this count, because our decision on that issue will affect whether Defendants may be retried. United States v. Dipentino, 242 F.3d 1090, 1096 (9th Cir. 2001). After reviewing the record, we hold that the evidence was insufficient to support a conviction under 18 U.S.C. § 371. Therefore, the government may not retry Defendants on count one. Richardson v. [755]*755United States, 468 U.S. 317, 323-24, 104 S.Ct. 3081, 82 L.Ed.2d 242 (1984).
2. Pinkerton Liability
Because we reverse the conspiracy conviction, those counts that rested solely on Pinkerton liability must be reversed. However, as an alternative to Pinkerton liability, the district court gave instructions on aider and abettor liability. Under Ola-no, we “need not reverse if we find beyond a reasonable doubt that the jury would have convicted [the defendants] of each substantive count as aiders and abettors or as principals, and did not rely on Pinkerton.” 62 F.3d at 1199 (citation and internal quotation marks omitted). However, not all Defendants were named on all counts in this case. The superseding information included a general Pinkerton charge against all Defendants, but no general aiding and abetting charge. A defendant cannot be convicted of a crime with
which he or she has not been charged. See Stirone v. United States, 361 U.S. 212, 217, 80 S.Ct. 270, 4 L.Ed.2d 252 (1960) (describing general rule that “a court cannot permit a defendant to be tried on charges that are not made in the indictment against him”). Accordingly, in this case we can affirm a conviction under this rule only if the defendant was named in that count.
We reverse and affirm as set out in the chart below.4 We affirm only those counts in which Defendants were named and for which we conclude, beyond a reasonable doubt, that the jury would have found Defendants guilty without the Pinkerton instruction.5 In other words, we affirm those counts for which the jury undoubtedly would have convicted the defendant as a principal or as an aider or abettor without a Pinkerton instruction. Olano, 62 F.3d at 1199.
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3. The Expert Testimony
Reviewing for abuse of discretion, Gen. Elec. Co. v. Joiner, 522 U.S. 136, 141, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997), we conclude that the district court did not err by admitting expert testimony on the relationship between pimps and their prostitutes. See United States v. Taylor, 239 F.3d 994, 998 (9th Cir.2001) (concluding that it was not an abuse of discretion to [756]*756admit similar expert testimony for the same purpose). The expert also did not impermissibly vouch for the government’s witnesses. See United States v. Kearns, 61 F.3d 1422, 1427 (9th Cir.1995). We need not reach the question whether the district comet should have conducted a Daubert hearing prior to admitting the testimony, because none of the Defendants preserved that issue for appeal.
4. The “Other Acts” Evidence
We review for abuse of discretion the district court’s admission of “other acts” evidence. United States v. Palmer, 3 F.3d 300, 303-04 (9th Cir.1993).
(a) Inadequacy of Notice to Present Rule I0k(b) Evidence
The notice requirement of Federal Rule of Evidence 404(b) is not stringent. The notice may be general. See Fed.R.Evid. 404(b) advisory committee’s note, 1991 amends, (stating purpose of requirement is to “reduce surprise and promote early resolution on the issue of admissibility”).
Here, the notice requirement was satisfied. The government provided several pretrial notices of their intention to introduce Rule 404(b) evidence. Defendants responded with motions in limine, and the court ruled before trial that the evidence was admissible. The intended function of the notice requirement was served.
(b) Admissibility of the “Other Acts” Evidence
We apply a four-part test to gauge the admissibility of “other acts” evidence under Rule 404(b). United States v. Chea, 231 F.3d 531, 534 (9th Cir.2000). The district court did not err. Evidence of other acts of pimping, even violent acts, are properly admitted in Mann Act prosecutions to demonstrate modus operandi, motive, and intent. United States v. Winters, 729 F.2d 602, 604 (9th Cir.1984). Further, the district court permissibly concluded that the probative value of the evidence was not substantially outweighed by the danger of unfair prejudice. The district court sua sponte instructed the jury several times that it was to consider such evidence for a limited purpose and it limited exceptionally prejudicial testimony.
In sum, although the evidence of other acts was considerable, it was not an abuse of discretion to admit it.
5. Ineffective Assistance of Counsel
“A challenge to a conviction based upon ineffective assistance of counsel ordinarily is made through collateral attack, not on direct appeal.... ” United States v. Cochrane, 985 F.2d 1027, 1029 (9th Cir.1993) (per curiam). This case does not present the kind of exceptional circumstances under which we would reach the claim on direct appeal. See United States v. Ross, 206 F.3d 896, 900 (9th Cir.2000) (stating exceptions). We therefore decline to reach this'issue.
B. Individual Arguments
1. Sufficiency Challenges
Defendants allege that the evidence was insufficient to convict them of several of the substantive counts. Johnson argues that the evidence was insufficient to support the verdict against him on counts 10 and 12. McMillion and Sallis allege that the evidence was insufficient to support the verdict against them on counts 11 and 22. Thompson contends that the evidence does not support a conviction on counts 5, 10, 12, and 22. We have reversed some of these convictions because the facts of the case indicate no possibility at all of aiding and abetting liability. Therefore, we consider Defendants’ challenges only as to the counts that remain: count 12 as to John[757]*757son, counts 11 and 22 as to McMillion, and counts 5 and 22 as to Thompson.
On count 12 for Johnson, the evidence, viewed in the light most favorable to the government, showed that McMillion, in Billings, called Johnson, in Seattle, and Johnson told McMillion that “it would be a good [prostitution] business up there [in Seattle}.” McMillion later drove juvenile R.D. to Seattle. “To be guilty of aiding and abetting another person, it is necessary that the defendant in some sort associate himself with the venture, that he participate in it as something that he wishes to bring about, that he seek by his action to make it succeed.” United States v. Vasquez-Chen, 978 F.2d 546, 552-58 (9th Cir.1992) (internal quotation marks omitted). This evidence is not sufficient to prove that Johnson aided and abetted in the transportation of R.D. from Montana to Seattle with the intent that R.D. engage in prostitution. Johnson gave no specific counsel or direction about how to engage in prostitution in Seattle. It cannot fairly be said that Johnson provided any particular information about how McMillion might operate with a prostitute in Seattle. From the record, we can only conclude that McMillion knew how to be a pimp with a prostitute, and the statement by Johnson about prostitution being a good business in Seattle is not the type of counsel or encouragement that, without more, can create criminal liability.
As to McMillion and Thompson, viewing the evidence in the light most favorable to the verdict, the evidence was sufficient to permit a rational fact-finder to conclude beyond a reasonable doubt that Defendants were guilty on those counts.
2. McMillion, Sallis, and Thompson: The Selective Prosecution Rulings
In order to obtain discovery in support of a theory of selective prosecution, a defendant must make a “credible showing of different treatment of similarly situated persons.” United States v. Armstrong, 517 U.S. 456, 470, 116 S.Ct. 1480, 134 L.Ed.2d 687 (1996). After a hearing, the district court determined that Defendants had failed to make such a showing. After reviewing the evidence, we hold that the district court did not abuse its discretion in preventing Defendants from seeking discovery on a selective prosecution theory.
Before trial, the court issued an order barring evidence of selective prosecution. Defendants allege that in so doing, the district court denied them their rights under the Confrontation Clause by “prohibiting them from mentioning or examining any witness on the issue of racial prejudice.” The court’s order did not bar cross-examination as to racial bias. The order does not say that Defendants could not question witnesses about whether the witnesses had a bias against a particular race. Thus the premise of this argument is incorrect, and no violation of Defendants’ confrontation rights is shown.
3. McMillion: The Motion to Suppress Evidence From the Stop of McMil-lion’s Car
McMillion argues that the district court erred when it denied a motion to suppress evidence from an automobile stop in July of 1999. From this stop, officers learned the identity of victim M.D., who later told officers that McMillion and Thompson had attempted to recruit her as a prostitute.
The stop was supported by reasonable suspicion. The officers had an objectively reasonable belief that criminal activity was afoot based on their surveillance of McMilhon’s car. The officers saw someone who looked very young, accompanied by a known prostitute, get into a car driven by a suspected pimp. Those facts provided reason to suspect the pimp of [758]*758transporting a minor for the purpose of prostitution. Therefore, the motion to suppress was properly denied.
C. Sentencing Issues
1. McMillion and Sallis: Erroneous Statutory Máximums Applied to Counts 2, 3, 10,11, and 12
The October 1998 amendments to the Mann Act increased the applicable statutory máximums. The amendments also provided for an increase in the statutory maximum for offenders who had been previously convicted of a sex offense. 18 U.S.C. § 2426. The máximums applicable to pre-October 1998 and post-October 1998 conduct are set out below. The enhanced recidivism increase for prior sex offenses, applicable here to defendant Sal-lis, is the number in parentheses in the third column.
The district court sentenced McMillion and Sallis under the amended máximums.6 The government concedes that this was error, and we agree. Counts 2, 3, 10, 11, and 12 covered conduct that took place before October 1998. See Appendix. We have already reversed several of these counts because of the conspiracy issues. Those that remain are McMillion’s convictions on counts 10,11, and 12.
Count 12 is based on 18 U.S.C. § 2423(a), which as indicated had an applicable statutory maximum of 120 months. McMillion, however, received a sentence of 120 months on counts 10 and 11,’ and 180 months on count 12, all of which are over the statutory máximums. We reverse and remand these three counts as to McMillion for resentencing under the pre-amendment statutory máximums.
2. McMillion, Thompson, and Sallis: The U.S.S.G. § 3A1.1 Enhancement for Vulnerable Victims
The district court erred in imposing a vulnerable-victim enhancement for two of the victims in this case, R.K. and R.D. See United States v. Castaneda, 239 F.3d 978, 981 (9th Cir.2001) (holding that in order for the vulnerable-victim enhancement to apply to Mann Act offenses, the victim must be vulnerable to a degree beyond that already contemplated by the offense). An enhancement for victim vulnerability still would be appropriate if the district court makes a finding of unique vulnerability in the particular circumstances. United States v. Williams, 291 F.3d 1180, 1195 (9th Cir.2002).
R.K. and R.D. were the victims of the following counts: 2, 3, 5, 9, 10, 12, and 13. We have affirmed McMillion’s convictions on counts 10, 12, and 13 and Thompson’s conviction on count 5. The other counts have been reversed as to all three Defendants who raise this issue. As for MeMil-lion, we reverse and remand for resentenc-ing on counts 10, 12, and 13, the remaining counts that pertain to R.D. As for Thompson, we reverse and remand for resentenc-ing on count 5, the remaining count involving R.K.
3. Sallis and McMillion: The Upward Departures
The district court departed upward in sentencing Sallis and McMillion. The court departed upward seven levels in sen[759]*759tencing McMillion. Sallis’ departure was achieved by imposing a consecutive sentence for the conspiracy count. We affirm the departure in McMillion’s case.
(a) McMillion
The district court departed upward seven levels to take into account McMillion’s extreme conduct. See U.S.S.G. § 5K2.8. This departure is supported by the record and is reasonable. The victims testified that McMillion engaged in exactly the kind of extreme “degrading” and “humili-atfing]” conduct that U.S.S.G. § 5K2.8 contemplates would warrant a departure.
(b) Sallis
Sallis’ argument is no longer relevant because we have reversed the conspiracy count, and thus necessarily he will no longer serve a sentence on that count that is consecutive to his sentences on the other counts. Should the district court consider a departure on remand, it should follow the notice requirements set forth in Williams.
CONCLUSION
As for defendant Johnson, we REVERSE his convictions on all counts.
As for defendant Sallis, we REVERSE his convictions on counts 1, 2, 8, 5, 9, 10, 11, 12, 13, 18, and 19. We AFFIRM on counts 16, 17, 20, and 21. We REVERSE and REMAND for resentencing so that the sentence on these counts will not be affected by grouping provisions relating to the reversed counts.
As for defendant McMillion, we REVERSE his convictions on counts 1, 2, 3, 5, 9, 16, 17, 18, 19, 20, and 21. We AFFIRM on counts 10, 11, 12, 13, and 22. We REVERSE and REMAND for resentenc-ing so that the sentence on these counts will not be affected by grouping provisions relating to the reversed counts. We also REMAND for resentencing because the district court applied the wrong statutory maximum to counts 10, 11, and 12. We also REMAND for resentencing on the vulnerable-victim enhancement in the light of Williams.
As for defendant Thompson, we REVERSE his convictions on counts 1, 2, 3, 10, 11, 12, 13, 16, 17, 20, and 21 and AFFIRM on counts 5 and 22. We REVERSE and REMAND for resentencing so that the sentence on these counts will not be affected by grouping provisions relating to the reversed counts. We also REMAND for resentencing on count 5 for the purpose of reconsidering the vulnerable-victim enhancement in the light of Williams.
APPENDIX7
Count (18 U.S.C.) Date Conduct Charged Victim Disposition
1— § 371 Before Dee. 1994 to after Auor. 1999 Conspiracy N/A Reversed.
2— § 2422(a) March, April 1998 Persuasion, etc. R.K. Reversed.
3— § 2423 March, April 1998 Transport of minor R.K. Reversed.
5— § 2422(a) July 1999 Attempt8 to persuade, etc. R.K. Affirmed as to Thompson.
[760]*760Reversed as to all others._
9— § 2422(a) Before August 1998 Attempt to persuade, etc. R.D. Reversed.
10— § 2422(a) August 1998 Persuasion, etc. R.D. Affirmed as to McMillion. Reversed as to all others.
11— § 2421 August 1998 Transport R.P. Affirmed as to McMillion. Reversed as to all others.
12— § 2423(a) August 1998 Transport of minor R.D. Affirmed as to McMillion. Reversed as to all others.
13 — § 1952 August 1998 Crime of violence to further unlawful activity R.D. Affirmed as to McMillion, Reversed as to all others.
16— § 2422(a) January 1999 Persuasion, etc. K.M. Affirmed as to Sallis. Reversed as to all others.
17— § 2421 January 1999 Transport K.M. Affirmed as to Sallis. Reversed as to all others.
18— § 2422(a) Summer of 1998 Attempt to persuade, etc. T.D. Reversed.
19— § 2422(a) Summer of 1998 Attempt to persuade, etc. N.L. Reversed.
20— § 2422(a) Winter of 1999 Persuasion, etc. L.B. Affirmed as to Sallis. Reversed as to all others.
21— § 2423(a) Winter of 1999 Transport of minor L.B. Affirmed as to Sallis. Reversed as to all others.
22— § 2422(a) July 7,1999 Attempt to persuade, etc. M.D. Affirmed as to Thompson and McMillion. Reversed as to all others.
This disposition is not appropriate for publication and may not be cited to or by the courts of this circuit except as may be provided by Ninth Circuit Rule 36-3.