HTTP Error 500.21 error while deployed using iis 7

Solution

1 Rrun the command prompt (administrator)
2. Put below line in the command prompt and press enter 

It will install asp.net 4 to resolve the issue

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

or

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