Is a district court's decision not to admit evidence within the scope of the Federal Rule of Evidence 404(b) reviewed de novo?

A district court's decision whether evidence falls within the scope of the Federal Rule of Evidence 404(b) is a question of law which is reviewed de novo. United States v. Mundi, 892 F.2d 817, 820 (9th Cir.1989), cert. denied, 111 S.Ct. 1072 (1991). A district court's decision to admit evidence is reviewed for abuse of discretion. United States v. Soliman, 813 F.2d 277, 278 (9th Cir.1987). Similarly, a district court's decision to limit the scope of cross examination is reviewed for abuse of discretion. United States v. Changa, 901 F.2d 741, 743 (9th Cir.1990). Even where a trial court has abused its discretion, the reviewing court must determine whether the error was harmless beyond a reasonable doubt. Delaware v. Van Arsdall, 475 U.S. 673, 681 (1986).