Asp Submitted

I have an user.asp page(has html display) which displays
the controls; After client-side validations, I do a
document.form.submit() to a process asp page(no html, only
server side processing and then redirects to the user.asp).
This process asp calls some dll functions which might take
a couple of hours if number of records to process is huge.
Now, the dll opens a pop-up window which shows the status
of the results(number of records processed and failed).
After exactly 1 hour, the user.asp page says page cannot
be found. Is it due to some timeout or something? What
could be the reason?