In what circumstances will a federal court vacate a defendant's guilty plea under Rule 11 of the Criminal Code?

We therefore strike a balance between requiring strict adherence to the provisions of Rule 11 and disregarding variances from the rule that do not affect defendant's substantial rights. In some cases, a combination of circumstances "tips the scale" in favor of vacating defendant's guilty plea even though one mistake standing alone could be harmless error. See United States v. Ferrara, 954 F.2d 103, 108 (2d Cir. 1992); see also United States v. Livorsi, 180 F.3d 76, 82 (2d Cir. 1999). In Ferrara, we vacated defendant's guilty plea where the district court failed to warn him that he had no right to withdraw his plea even if the court did not accept the plea agreement's sentencing recommendation, and the plea agreement itself was unclear regarding the government's sentencing recommendation. See Ferrara, 954 F.2d at 104-08. In Livorsi, we vacated defendant's guilty plea where the district court failed to give the same warning and also failed to ask defendant whether at the time of the plea he was under the influence of drugs or alcohol or in the ongoing care of a physician. See Livorsi, 180 F.3d at 82.