500.0 Internal Server Error - aspnet_isapi.dll failed in IIS 7.5

If you experience '500.0 Internal Server Error - aspnet_isapi.dll failed' even after trying all possibilities like 'aspnet_regiis -i' etc..., just uninstall IIS and Re-install again, it just works. It is Microsoft:)

I faced this when i installed Framework 4.0, so uninstalled IIS 7.5/Framework4.0 and re-installed both.

Error message when you visit a Web site that is hosted on IIS 7.5: "HTTP Error 404.17 - Not Found"

This article might help, but we need to look for three things particularly

configure the following settings to match the handler requirements:

• .NET Framework Version
• Enable 32-Bit Applications
• Managed Pipeline Mode

HTTP 500.0 - Internal Server Error in Windows 2008 R2 Server

After deploying a 32-Bit WCF service in IIS 7.5(Windows 2008 R2 server), browsing the service failed with
HTTP 500.0 - Internal Server Error, and from the error message i figured out something wrong with PageHandlerFactory. For 32-Bit web apps, it is mandatory to set 'Enable 32-Bit Applications' to 'True'. We can either set it @ 'Application Pool Defaults' or the specific Application Pool in question.