Today I Came across 500 error with “"Could not load all ISAPI filters for site 'SHAREPOINT CENTRAL ADMINISTRATION V4'. Therefore site startup aborted” in the Event Log. This happened after I installed .Net Framework 1.1 (32bit) ( Wanted to test one application which was built on .Net Framework 1.1).
After installing .Net Framework 1.1, My none of sites were working including Central Admin. Event Log had below entries
1) ISAPI Filter ‘C:\Windows\Microsoft.NET\Framework\v4.0.21006\aspnet_filter.dll’ could not be loaded due to a configuration
2) Could not load all ISAPI filters for site ‘SHAREPOINT – 80’. Therefore site startup aborted.
3) Could not load all ISAPI filters for site ‘SHAREPOINT CENTRAL ADMINISTRATION V4’. Therefore site startup aborted.
After Searching and looking at log I could understand that my ISAPI setting had conflict with .Net Framework 1.1 installation (32 bit and 64 bit).
1) Un-Installed the .Net Framework 1.1 ( any how is it not required now)
2) re-register Asp.net 2.0 as default by running below command
And All started working like before!!