Hello Peacemaker,
When you try to install an update for the .NET Framework 1.0, 1.1, 2.0, 3.0, or 3.5, you may receive Windows Update error code "0x643" or Windows Installer error code "1603"
RESOLUTION
To successfully install the update, uninstall all the versions of the .NET Framework on the computer, and then reinstall all the versions of the .NET Framework on the computer. You may have to work through more than one of the following methods.
Method 1: Manually remove and reinstall .NET Framework
To manually remove and reinstall the .NET Framework, follow these steps:
1. Remove the .NET Framework.
1. Click Start, and then click Control Panel.
2. Double-click Add or Remove Programs.
3. Note each version of the .NET Framework that is already installed on the computer. Then, uninstall all the versions of the .NET Framework.
4. When you are prompted, restart the computer.
Method 2. Use the Windows Installer CleanUp Utility to clean up the MSI database state for all the versions of the .NET Framework.
1. Download the Windows Installer CleanUp Utility. The following file is available for download from the Microsoft Download Center:
http://download.microsoft.com/download/e/9/d/e9d80355-7ab4-45b8-80e8-983a48d5e1bd/msicuu2.exe
2. Install the Windows Installer CleanUp Utility as an administrator or as a user account that is a member of the local Administrators group.
3. Click Start, point to All Programs, and then click Windows Install Cleanup.
4. In the Windows Installer CleanUp Utility, remove all Windows Installer applications for the .NET Framework.
3. Restart the computer.
Download and then reinstall all the versions of the .NET Framework that were previously installed on the computer.