Use the .NET Framework Cleanup Tool to uninstall multiple versions of the .NET Framework, and then reinstall the components.To do this, follow these steps:
Check out the .NET Framework Cleanup Tool User’s Guide.
Download the .NET Framework cleanup tool.
When you are prompted, click Open, and then click Extract Now.
In the files that you extracted, double-click cleanup_tool.exe.
If you are prompted for an administrator password or for confirmation, provide the password, and then click Continue.
In the Do you want to run the .NET Framework Setup Cleanup Utility? message, click Yes.
Click Yes to accept the license agreement.
In the Product to cleanup window, click the list, select .NET Framework – All Versions, and then click Cleanup Now. Note The cleanup tool does not let you remove the .NET Framework 2.0 in Windows Vista or later versions of Windows because the .NET Framework is installed as an operating system component.
After the .NET Framework is removed, restart the computer.
Download and install the following components:
The .NET Framework 1.1The .NET Framework 1.1 Service Pack 1 (SP1)
The .NET Framework 3.5 Service Pack 1 (this will also install the .NET Framework 2.0 SP2 and the .NET Framework 3.0 SP2)
Restart the computer.
Visit Windows Update again, and then check for and install updates.