windows error

[charles day]

running fp 5.0  on  XP networked to a cpu running '98.

Customer occasionally gets an error message. The processing will run 
sometimes for days without the error, then the error will occur.  
Customer  X's   the XP window,  then goes back into filePro and the 
error will not necessarily occur the next time the process is run and 
may not occur for days again.

message to the effect:

instruction @ blah-blah-blah can not be read

what does this have to do with filePro code and how can I find out where 
and why windows is having a fit?
what should I look for  in  filePro  code or settings that might cause 
this or allow it to happen?

charles day