Ge fanuc cpu341 90-30- commreq frequency too high

Hi everyone,
I have been facing the problem of encoder (1024 ppr) not reaching to its desired position while in auto mode.
The PLC fault table shows “Mailbox queue full- Comm_Req aborted”-- COMMREQ Frequency Too High –

%S9 is getting set frequently even after resetting the same.
There are 2 backplanes of 10 slots.
(1) PW 321 ,CPU341, PCM301, CMM311,APU300 , APU300
(2) PWR321 ,MDL645, MDL645, MDL645, MDL645,MDL930, MDL930, MDL930, MDL930, MDL930, MDL930.



Kindly guide me for resolving the issue.

COMMREQ instructions should be triggered by one-shots. You should not trigger another until the first has completed.