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 received the above error after installing .NET 1.1 and After uninstalling .NET 1.1 I still had the same error.However, the error has gone immediately after I went to IIS Manager -> ISAPI filters and removed the only filter from here (it was ASP.NET_4.0.30319.0),which is not the ideal fix.
Cause :
The ISAPI path has an extra ‘\’ character.
Resolution :
1. Open Internet Information Services
2. Click on the computer name on the left list.
3. Double-click on ISAPI Filters
5. Expand the columns as required looking for an Executable path with \\ in it, then click Edit:
5. Modify the ASP.NET_4.0_32bit executable path to not include a double ‘\’
6. Close IIS Manager and restart IIS from the command prompt (Start -> Run -> iisreset)
From the above screenshot, change the \\ to \ so the path reads:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_filter.dll
After clicking OK, all my testing started to work again and the 500 Internal Server errors went away.
Conclusion: A possible Microsoft update (exact cause unknown) made an error updating an existing or installing a new ISAPI handler to IIS. By mishandling the path, it inserted \\ instead of \ into the executable path causing IIS to be unable to load the filter.
This caused 500 Internal Server errors to sites/applications running application pools in 64bit mode.
Ref : https://sysadminspot.com/server-administration/isapi-filter-cwindowsmicrosoft-netframeworkv4-0-30319aspnet_filter-dll-could-not-be-loaded-due-to-a-configuration-problem/