Protools 7.4.2, Digi 002, MPC2000XL SPDIF

Anybody have any idea why my Digi 002 would be inconsistent with picking up a SPDIF signal from my mpc 2000XL/ Sometimes I make a session for a quick 2 track and it picks up the stereo SPDIF signal. Other times I start a session and the input area says SPDIF na (in italics). After checking preferences and starting a new session it will often later give me the option to select SPDIF for an input but won't detect any signal. Any advice would be greatly appreciated, I understand most of the time this type of stuff is usually user error. I guess my second question is if anyone has had the SPDIF connections in in their MPC go bad? If so how would one test them if the only other piece of gear I have is the Digi 002 listed above?