Please go through this post.
From the post:
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Click Start -> All Programs -> Accessories -> Run
In the Open textbox paste in the following line (see list of all .NET Framework version install, repair and unistall command lines here):
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
2. Click OK to start the repair.
3. After, the repair ran for a few minutes, I restarted IIS 7.5, and things began to work correctly!