Error 643 or 646 Windows update failed to install important updates.

You may receive this error when trying to install the following updates:

• Microsoft® .NET framework 1.1 SP1
• Security Update for Microsoft .NET Framework, Version 1.1 Service Pack 1 (KB928366)

Follow the procedure below to resolve the issue:

1. Use the Windows Installer CleanUp Utility to remove the Microsoft .NET Framework software.
2. Restart the computer.
3. Download and install the following software from the Microsoft Web site.
   • Microsoft .NET Framework Version 1.1 Redistributable Package
   • Microsoft .NET Framework 1.1 Service Pack 1
   • .NET Framework 1.1 Service Pack 1 SYSTEM.WEB.DLL and MSCOREE.DLL Security Update for Windows Vista
4. Run Windows Update to install the Security Update for Microsoft .NET Framework, Version 1.1 Service Pack 1 (KB928366).