I had this same exact problem. I had the C-Lan board replaced which did not work. There was a QPPCN 969DR to upgrade our Tone Clock and they also replaced our Processor Interface Card for free which did appear to work. Prior to this Avaya did the following things for us to repair this issue is change the medpro and hub port to 100/half, change out each wiring harness from Cat 3 to Cat 5, upgrade the firmware on the C-Lan and Medpro board to the latest release, they replaced our Main System Processor as well. We spent tons of time (5 months) troubleshooting this problem. Hopefully all these tips will help you.