I was recently setting up IIS 7.5 on Windows 2008 R2 for an ASP.NET site and came across the following 500 error:

Handler “PageHandlerFactory-Integrated” has a bad module “ManagedPipelineHandler” in its module list.

After a bit of searching, it turns out ASP.NET was not completely installed with IIS even though I checked that box in the “Add Feature” dialog. I found a number of suggestions but found this command. It fixed my issues and got rid of the error.

%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe -i 

For a 32 bit system, use the following command.

%windir%\Microsoft.NET\Framework\v4.0.21006\aspnet_regiis.exe -i