I found when using Kohana in FastCGI mode that I was getting error 500 messages without the usual stack trace or error message. This was only happening when I accessed the development server remotely, not when I ran it locally (i.e. http://localhost/). Turns out this is actually the default behaviour for IIS7 with FastCGI. To change this you simply run the following command:
%windir%\system32\inetsrv\appcmd.exe set config -section:system.webServer/httpErrors -errorMode:Detailed
All fixed! If you want to change it back when you put the server into production then change the errorMode to “DetailedLocalOnly”.