user32.dll question

I have an unknown problem with one of my applications. It has worked on numerous pc's (95/98/nt) but, on two pc's in particular the application repeatedly locks up. There are no error messages and lacks an identifiable pattern. I have been careful about memory leaks and cleanup. With a debugging tool I have been able to narrow the lockup to a subroutine which makes several api calls.

I don't know if the problem is the user32.dll version or not. My system as well as at least one other pc on which the app works, have a much newer version of the dll. How would I replace this dll which the system is using, should I replace it (will I do damage elsewhere??), or am I going down the wrong path??

any suggestions and help is greatly appreciated!

E