Latest news:
The client has removed the Windows "temp" folder from NAV auto-protect. The reporting problems have disappeared for the past 3 days!!!
The problem appears to be caused by the latest version of Norton Corporate Anti-Virus (Version 9).
However, their I.T. consultant is skeptical. He is also concerned about the security risk this solution poses. So he is going to do more tests!
If there are any new developments, I will post them.