- Click Start -> run -> cmd - ENTER
- At the command prompt, type the following, and then press ENTER:"%windir%\Microsoft.NET\Framework\version\aspnet_regiis.exe" -i
- Register the Aspnet_isapi.dll by clicking start -> run
- In the Open text box, type "regsvr32 %windir%\Microsoft.NET\Framework\version\aspnet_isapi.dll" and then press ENTER
In both of the above paths, version is the directory that corresponds to the version of .NET that you installed.
The original Source of this information is Mike Viehweg's site.