When following error comes during browsing of any website directly from iis, it means our .net framework is not registered with our installed iis. I have faced this issue while installing "Umbraco" cms.

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

Solution :Its solution is very simple. Just register your .net framework with IIS.Run Following command on your command prompt.

windows/Microsoft.NET/Framework/v4.0.30319/aspnet_regiis.exe -i

It will install framework 4.0 (choosen one) on your IIS and your targetted websites will work fine.
Thats all :)
Happy Coding !!!