Inaccurate results in performance counters of ASP.NET!
The latest entry in Microsoft Knowledge Base article explains about a BUG: Performance counters may have inaccurate results when a user without permission runs the ASP.NET worker process. Some resolution is provided to resolve this problem.
Navigate to Microsoft Knowledge Base Article - 841554
for more details.
I was encountered with this problem during performance testing of one of our projects. We found the same solution in one of newsgroups and resolved the problem. That's the power of newsgroups.