United States v. Monzon, 429 F.3d 1268 (9th Cir. Dec. 7, 2005) (conviction and sentence for possession of a firearm in furtherance of a drug trafficking crime reversed where the court committed plain error when it accepted guilty plea in violation of Federal Rule of Criminal Procedure 11, because court failed to establish a factual basis for believing that the defendant possessed the firearm at least partly for the purpose of protecting the drugs, where the defendant factually denied that intent during the plea colloquy, and the error affected defendants substantial rights, defined as a reasonable probability of a different outcome sufficient to undermine confidence in the outcome).
http://caselaw.lp.findlaw.com/data2/circs/9th/0330497p.pdf