Intermittent P-ROC NOT FOUND error

[msadan]

When powering the game up I'm getting an intermittent P-ROC NOT FOUND PLEASE CHECK CONNECTION & POWER error message. Sometimes it will boot up normally on the first try, sometimes I have to cycle the power several times before it will find the P-ROC. Usually after it boots up successfully it will be okay but a few time it has displayed the P-ROC NOT FOUND message during game play. I've re-seated connectors, tried moving the USB cable to a different port, and tried a different USB cable, no help. Any ideas on what to check next?

[sdtom]

Try pressing in (gently) the 3 proc boards mounted to the playfield to help seat them.