The Killer - S1-E1
Other mistake: We are of course not privy to the protocol of the secret service organization Jim Phelps is a member of; however, while he is at his own place choosing at his leisure the team members, Jim to pick Nicholas types "KJ" on the laptop, to pick Casey he types "PK", then to pick Max and Grant he just clicks a TV remote. Whatever system they are using, does not seem to make any internal sense.
The System - S1-E2
Other mistake: When Nicholas impersonating Marley is going through the security cameras of the casino (none of which catching the 'double Marley' on camera exposing the trick, conveniently) there is one that follows with a cinematic motion the exact movements of the person answering the phone. They are all static cameras, just that one arbitrarily moves, without Nicholas doing anything. (00:36:50)