COMM ERROR in general refers to network communications. Is there an external control module with a twisted pair buss wires? As stated before, check powers and grounds, but also check anything relative to buss network wiring. Anything that will stop any talking to the rest of the system (ie: throttle bodies) should be suspect. After that, it is usually an internal controller failure.
Note: This is all my opinion from my experience as a Level 3 Chrysler Tech and shop foreman.
An MSD can probably interfere with it as well if its close by or the wires for it are.
