This tool detects and tries to fix some frequently occurring issues with the setup of or with updates to the Microsoft .NET Framework.
This tool troubleshoots common issues with the setup of or with updates to Microsoft .NET Framework setup installation. Additionally, this tool tries to resolve these issues by applying known fixes or by repairing the installed product.Note: The current version of the tool supports repairing the .NET Framework 4, this will be extended to include other versions of the .NET Framework in the future.
Supported operating systems: Windows 7, Windows Server 2003, Windows Server 2008, Windows Vista, Windows XP
http://www.microsoft.com/en-us/download/details.aspx?id=30135