OMRON PLC - Intermittent crashing

Hi,
This is my 1st attempt at any forum so please excuse any ??? I have a CVM1-CPU21-V2 system that is randomly crashing (typically 10 times / week). The PLC error code is 80F1 I/O bus error 2200. I hoped this would point to the offending module but have been unable to find the relevent info. Can anyone point me in the right direction? (I've trawled the manuals to no avail) PS we have no spares so cannot fault find by replacing cards. All contacts cleaned (appropriate aerosol) but no change.
Thanks (in anticipation)

Hello Willie.uk,
Welcome to the Forum!
According to the manual that I have here, error code 80F1 is a Fatal Memory Error...
"An error has occurred during check of the PLCor EM Unit memory, or program transfer could not be completed at start up"
When the 'crash' occurs, what is the value in A400, and are there any bits ON in A401 or 402?
As a further guide (if you are certain that it's an IO error), A404 bits 0 - 7 contain IO bus error slot number, bits 8 - 15 contain IO bus error rack number.
A405 contains CPU Bus Unit error unit number.

Hope this helps.

Thanks for your prompt reply. The PLC is fitted 20miles away, so its going to be later this week before I can get back to this job (due to high work load and this PLC "normally" restarts after a short rest; plus they are not shouting as loud as others). Impressed by responses, better than I expected