APPCRASH SO/IM/MF

2 weeks ago we upgraded to Sage 2013 October MRU and Citrix 7.5 (2008 r2). We run DC Warehouse so we are unable to upgrade any further at this time. Some users have been experiencing an intermittent generic APPCRASH.. So far it seems to occur in SO sozdj101.exe, MF mfzdb001.exe and IM (rarely)..  mfzdb001.exe has been customized and the other two have not. We are unable to recreate the error and can go a full day without hearing about it. Sometimes all of the user has to do is enter the WO# or SO#  and hit tab then BOOM. This crash has occurred outside of the virtual Citrix environment  which eliminates any server related memory leaks & hot fixes.

I have updated permissions in the registry for the state of the art key, folder permissions for the Sage install, recreated user profiles, MAS500 profiles, replaced the workstation/thin client..

I can't seem to find any info on this.. Anyone have any other ideas I could try?