HTTP Error 500.21 - Internal Server Error Handler "PageHandlerFactory-Integrated" has a bad module "ManagedPipelineHandler" in its module list. pelineHandler" in its module list.

To repair this problem I ran a full silent repair of the .NET Framework 4.0.   Here's how on either a 32 bit or 64 bit computer:

1. Click Start -> All Programs -> Accessories -> Run
2. In the Open textbox paste in the following line (see list of all .NET Framework version install, repair and unistall command lines ):
   For silent repair on 32 bit computer with .Net Framework version 4.0.30319 use:
   

   %windir%\Microsoft.NET\Framework\v4.0.30319\SetupCache\Client\setup.exe /repair /x86 /x64 /ia64 /parameterfolder Client /q /norestart

   For silent repair on 64 bit computer with .Net Framework version 4.0.30319 use:
   

   %windir%\Microsoft.NET\Framework64\v4.0.30319\SetupCache\Client\setup.exe /repair /x86 /x64 /ia64 /parameterfolder Client /q /norestart

3. Click OK to start the repair
4. After, the repair ran for a few minutes, I restarted IIS 7.5, and things began to work correctly!

 Hopefully, that will work for you...
Some people also seem to be having success correcting this error by running aspnet_regiis.exe. I initially tried this and it did not work for me, but feel free to give it a shot. (Keep in mind for the example below I have .Net Framework version 4.0.3.0319 installed on my computer, but you may need to change directory version to what is installed on your computer):  Here's how to run aspnet_regiis.exe:

1. Run "aspnet_regiis.exe" program from command line (within Command Prompt):

%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe –i

If you want to open it using the Run program, just type in "Run" in the Windows 7 search box, then use the following line below in the Open box, then click OK:

%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe –i

 Note if your computer is 64 bit, then I would change the line to:

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

Hopefully, these solutions help get you up and running and fix the IIS7 error...  Handler "PageHandlerFactory-Integrated" has a bad module "ManagedPipelineHandler" in its module list.