I assume that all of the lines light up when you slect them? When you say that the system was taken off the wall, was anything altered with the wiring?
Lastly, do you hear the line card's relay click when the hold button is partially pressed? The only other thing that I can think to do is to disconnect any connections to the violet/green, violet/brown and violet/slate pairs that ONLY feed the 2565 sets. Do this one cable at a time and test each time you do this. It sounds as if maybe a 2565 is plugged in where a 2564 originally was.
Oh, a few more things: Do you hear the motor start running in the interrupter when you attempt to place a call on hold? Is the call actually being held with no lamp flash or does the call actually drop when placed on hold?
Sorry for so many questions but there are many things that could be causing this problem.
