Problem from Web Application Stress Tool

[Cissy]

Hi:

I am learning Web Application Stress Tool and try to run Sample Script. When
I tried to Add Counter under Perf Counters node, There is Error message:
Failed to load the perf counters from the computer ... If I click OK, The Add
counter to report window is pop-up, but Object is empty. I can't add any
counter such as Get Requests/sec.

When I run Performance, tried to add counters into System Monitor, All
counters are there. No problem to add any counter.

When I open .NET, Server Explorer, All counters are in the tree of
Performance Counters. After added new counters, no counter objects exist if I
run Web Application Stress Tool again.

Is anyone who can help me to solve this problem?

Thank you very much.

Cissy