I've had a similar experience with the ribbon cable connector (data lines).

I was asked to look at a DMC (dot matrix controller) exhibiting page errors. Sure enough display test shows page errors. I took the board home.

Put the board on my bench. Passes display test perfectly. Weird. Put the board in a machine and it passes the display test perfectly. Put the board back on my bench. Passes display test perfectly.

So I give the board back to the owner and well ... it works perfectly.

I call it "pinball voodoo".

If you have re-seated the ribbon cable and you know it's good (likely is but is not guaranteed to be due to being brand new) then take Chris Hibler's advice. It is very likely you have a problem in the digital logic section of the DMC board. If after replacing the SRAM the page errors still persist visit the Pinwiki page for WPC and you will find some more information on DMC page errors.

Good advice if the potential problem is in the digital logic section (as it is for this problem). I concur that you should try this if you want another data point.

For other higher voltage problems it can pose a risk of damage to the machine that is being used for testing. It's often safe but not always safe.