I think "using it to long" are the key words here. As John has suggested it could well be mermory resource issues that cause the problem.

I don't know if John is right in suggesting it is basically a DOS program - I had been under the impression that the CD version was a Windows program.

There are other resource issues with Windows in that the OS uses chunks of memory called system resources (user and GUI I think). Windows has varied in its handling of these resources, I know Win 3.1 used fixed 64K segments which could soon get eaten up and on the other hand some NT versions could use all availible memory. I'm not sure where 98SE sits on this but I think '95 improved on 3.1 and 98 made further improvemnts.

From a programmers side, in my very limited experience, when I have had programs that have been unstable and would suddenly lock or do wierd things, the root cause has either been failure to release resources (as John explained above, sooner or later you run out) or failure to allocate memory correctly. It is quite possible for example to assign values to dynamic variables (pointers) without first reserving memory for thier use. The net effect here is that you are writing to "unknown memory" and although things may appear OK for a while, believe me just about anything is possible! Again, as John has indicated, Windows is far more likely to "call foul" than DOS which will happily let you write anywhere until you bring the system to a grinding halt. An OS may also complain if you try to free up resources that you never allocated in the first place...

Jon