Microsoft Windows Error Code 643by Andrew Aarons
Microsoft updated technical support information for the .NET Framework in October 2010. Users downloading updates for the .NET Framework received error messages with the code "0x643" or "1603.
The 0x643, or 643, error message occurred with updates from Microsoft .NET Framework versions 1.0, 1.1, 2.0, 3.0 or 3.5.
According to Microsoft, the error code 0x643 is generic and is shown when an installation does not go correctly. Since you need to download .NET Framework files before you can install the updates, it's more likely the files have become corrupted. The other listed cause for a 0x643 error is as inconsistency in the MSI database.
The most common Windows-based problems can be resolved using the Microsoft Fix It Wizard. You can also try using different methods of installing the .NET Framework updates, such as downloading the update directly from the Windows Update website rather than letting Windows download it in the background. Finally, Microsoft provides a .NET Framework tool that removes multiple instances of the file. Download the tool and follow the on-screen prompts to remove the program. Reboot and reinstall the updates.