Method 1: Manually remove and reinstall .NET Framework
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To manually remove and reinstall the .NET Framework, follow these steps:
http://support.microsoft.com/kb/923100
Method 2: Use the .NET Framework automatic cleanup tool
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This tool is not intended as a substitute for the standard uninstall procedure. You should try to perform an uninstall by using the steps in Method 1, earlier in this article, before you use this cleanup tool.
http://support.microsoft.com/kb/923100