Micrologix 1100 configured as Modbus RTU Master, comms locking up

I have an application where I have a micrologix 1100 configured as a modbus RTU master, connected by an 1763-NC01 to a network of Telemecanique Tesys U motor starters. The majority of the time the communications performs very well but once every couple of months Channel 0 on the controller seems to lockup, Comms stops and will not restart unless i power cycle the PLC. It isnt any of the slaves that are causing the issue because i do not have to power cycle these.

Is there any way to unlock / reset the comms port without the customer having to power cycle the plc?

I assume you are getting a 37H error code on your MSG instruction when this is happening? The short answer is no, the buffers are filling up and the only way to reset them is a power cycle or download.
Previously we have had the same problem when communicating to multiple modbus devices (a single device does not seem to exhibit the same problems) with the 1100 but i found the lates firmware to be alot more stable. You can download it from here
http://www.ab.com/programmablecontrol/plc/micrologix1100/downloads.html