"Load report failed" after some report views

Hello everyone,
I'm using Crystal reports in my applications. It was working fine, but now it gives me some problems. After generating a few reports (don't know the exact number) it starts giving me the error message: "Load report failed".... it gives me this message for all reports, even those I have just viewed and proved they were working. 
It only stops when I do a "iisreset" in cmd.exe. Then it goes back to work, and after a fiew more views, it stops again.
What could it be?

Anyone?