After profiling a web application hosted in IIS, IIS may stop working altogether, even when not profiling, usually resulting in a page claiming "Server Application Unavailable" when accessed by a web browser.

A change was introduced in version 4.3 of ANTS Performance Profiler that can permanently affect the state of Internet Information Services when the web application needs to write files to a temporary directory. If ANTS Performance Profiler crashes, or you close it in task manager, the broken configuration remains. This will be addressed in a future version, but for now, there is a fix that should get IIS working properly again:

1. Run the Windows Registry Editor (regedit.exe)
2. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W3SVC
3. Delete the value called "Environment"