I got the following error on a 64 bit server:
ISAPI Filter 'C:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727\aspnet_filter.dll' could not be loaded due to a configuration problem. The current configuration only supports loading images built for a x86 processor architecture.
The error appears because on 64bit Windows, a given process like w3wp.exe can only load either 32bit DLLs or 64bit DLLs but not both types at the same time into the same process. The Enable32BitAppOnWin64 property indicates whether IIS creates 32-bit worker processes processes on 64-bit Windows.
The resolution is really simple, just run:
cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 0