‘INVALID CHASSIS ID’ - if getting the invalid chassis ID, and intermittent softkey functionality, on a SINGLE PFD installed aircraft, the PFD needs to be sent in for service. 
Generally, the Invalid Chassis ID message, will occur on dual PFD installed aircraft, is caused by a wiring issue. Check the wiring diagrams in the install manual 
and perform a continuity check on all the strapping wires.
 

PFD STRAPPING

PFD 1

PFD 2

Also, for single PFD installed with this message: