I put in a new engine and replaced the cpu and now it won't start

Yes it was.

Engine should start right up *provided* installation was completed correctly and no other ignition or fuel problems exists! .. Contact ECM supplier/programmers.

There was an error message that said passcode was incorrect.

Should have been pre-programed into replacement ECM... Dealer may be able to re-flash but don't know what it may cost... I'd contact whomever provided/programed the replacement ECM.

Thank you, we'll try that.