Stoping DOS application from crashing to desktop

I have a DOS application (BBX4 by Basis) that I use to run a filter
program on text files of up to 180 GB. Normally I have no problems with
the program, but occasionally it will suddenly quit with no error
messages and even telling it to stay open on close does not keep the
window open.
It is more likely to happen if I go into a Windows application like
FreeCell. If I keep the Window in focus it usually will complete. It
does not quit the same place as I can rerun it on the same files and the
next time it will complete.
I have tried to run it in compatibility mode with no change. I also set
the memory requirements to 8 MB with no change. Messing with the idle
sensitivity does not seem to make any difference.
Is there anything else I should look at. The program never crashed
under Windows 2000 and ran for several months under XP Pro before
starting this behavior.
Thanks for any ideas or assistance.