When profiling a web application hosted in IIS 5.x (Windows XP), the following error may occur before code profiling actually takes place:
Error stopping IISAdmin

Because the error occurs while stopping and starting IIS, the error message also covers a failure to START IISAdmin as well, so it is a good idea to check your application event log at this point. ANTS Performance/Memory Profiler will log the error actually returned by Windows at that location.

If the event log contains this entry:
System.Exception: Timed out starting 'IISADMIN'
the problem is actually a failure to start the service due to a timeout. In some cases, the default service timeout setting for Windows does not allow enough time for the service to start.

To increase the timeout, edit the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\WaitToKillServiceTimeout

The value of this registry key contains the number of milliseconds that Windows will wait for a service to start, the default being 30000 (30 seconds). Increasing this to 60000 (60 seconds) or slightly higher may allow the IISAdmin service to start successfully.

If you change the registry key, restart the computer so that the changes will take effect.