If you've ever tried to develop using PHP on IIS7 (Vista), you'll find that errors in your script result in the default IIS7 "friendly" HTTP 500 error page, which is useless for debugging. This happens in both FastCGI and ISAPI modes.
To save you hours of crawling through the 'net, the solution (found on this forum post) is very simple:
- Start a command prompt;
- Copy-paste the following: %windir%\system32\inetsrv\appcmd.exe set config -Section:system.webServer/httpErrors -errorMode:Detailed
- Run iireset
- Enjoy.