A customer has a Partner messaging module with a port expansion card in slot 5 of a 5 slot cabinet. The module has failed and been replaced 3 times over the last year. When the customer calls into the module (intercom 777), its just RNA. Resetting the system or reseating the module doesn't help. I replace it, it works for a few weeks/months then happens again. The processor module is R4, which works fine as well as the other modules in the cabinet. Any ideas as to what is causing this to repeat? I hate to throw money and parts at a problem at a 20 year old system, but the customer will not upgrade.

St Petersburg