1. Click the 'Start' button, then 'Run' and type 'msiexec/unregister' into the open field. This will un-register the Windows Installer. Click 'OK.' Click 'Start,' followed by 'Run' and type 'msiexec/regserver' into the Run box to re-register the Windows Installer.
2. Click 'Start,' then 'Run' and type 'cmd' in the Run box. Click 'OK' to open the Command window. Type '%InstallationPath%\dotnetfx.exe /t:%temp% /c:'msiexec.exe /fvecms %temp%\netfx.msi.' Press the 'Enter key.' Windows will perform a repair installation.

3. Launch the .NET Framework cleanup tool. Download the tool from the Windows Live website, and double-click the file to open it. The tool will automatically scan your system for . NET runtime errors and fix them.