I recently faced a problem in IIS 7, that when I was browsing any of the site hosted in my IIS, it was showing me an error message :
HTTP Error 500.0 - Internal Server Error
Calling LoadLibraryEx on ISAPI filter "C:\Windows\Microsoft.NET\Framework\v4.0.30319\\aspnet_filter.dll" failed
I tried several hit and tries like, I changed my application pool, removed my virtual directory and created new. But nothing worked for me.
Then I did some googling and found a post at :
http://forums.iis.net/t/1183736.aspx of kphani_prasad
Although it was not marked as answer but it solved my problem.
Steps which solved my problem :
1. Go to IIS.
2. Select your application from left pane, and click "ISAP Filters" from the right pane.
3. Check the path for which IIS is raising error. As in my case it was "v4.0.30319", and when I checked the path it was having an extra "\" (slash) in the path, so it was not able to load the desired dll file. I edited the path and removed extra "\" from the Executable path.
4. Restarted my IIS application and all was good to go.
Hope this help!