Conviction for resisting an executive officer by force or violence reversed where trial court improperly admitted prior encounters appellant had with police to prove knowledge. Appellant was found guilty of resisting an executive officer with force or violence (Pen. Code, § 69). On appeal he faulted the trial court for admitting prior incidents where he resisted police to prove his knowledge he was dealing with police rather than security guards in the present case, and to rebut mistake of fact. Held: Reversed. Section 69 requires proof the defendant knew he was resisting an executive officer in the performance of his or her duty. Generally, uncharged crimes are inadmissible to prove a defendant’s disposition to commit the charged offense (Evid. Code, § 1101, subd. (a)), but may be admitted for a non-character purpose, i.e., to show absence of mistake of fact (Evid. Code, § 1101, subd. (b)). Just as in cases where prior crimes are used to prove intent or common scheme, when the prior acts are used to prove knowledge, they must be sufficiently similar to the present crime to support an inference that what the defendant learned from his past experiences provided the requisite knowledge for the charged offense. Here the priors lacked probative value because they were dissimilar from the current offense in a material way, were cumulative, and were unduly prejudicial. The error was not harmless based on the prosecutor’s argument and the evidence.