Your question seems too vague to answer. Do you mean you put the shift in"D" and the transmission wont engage? Or do you mean the shift wont move out of Park?

The locking solenoid is in the SLA (Shift Lever Assembly), but from what I understand, failure of the Traction Control Relay output of the RCM will mean you can't shift from park.
Given that the RCM is home to at least FIVE failure modes of these cars, I'd be looking at the RCM first. That is, if I understand your post.