Has anyone installed a ABB M4M Network Analyzer? My Profibus Communication keeps freezing.

I got the comms(Profibus) going to the ABB M4M 20 fairly quickly, but it seems that the communication keeps freezing every now and then and its really frustrating. The only way to get the communication going again is to power cycle the M4M. The M4M doesn't freeze its real time values keeps changing, and in the ABB DCS Hardware structure the system status is healthy. No warnings or errors. We have installed 6 M4M Network analyzers on their own Profibus network with no additional devices. They freeze up one by one not all at the same time.

ABB 800xA System
CPU - PM866
Communication Module - CI854 (Profibus)
Baudrate - 500K (Was initially on 1.5M)

Has anyone encountered a similar problem?