Hello Razzgriz,
Thank you for using Microsoft Answers Forums.
Solution for code 643:
This is a common issue with the .NET Framework Updates.
http://support.microsoft.com/kb/923100
Follow the steps from the above web link to resolve the issue.
That should do the tirck for you.
Thank you.
Regards,
Augustine.
UDAY$012 Please let me know whether the solution worked or not, I appreciate and value your feedback. UDAY KUMAR