I'd suggest clicking here and following Chris instructions in the fifth post down. That's been the key for most people and should work for you.
Hope this helps,
John
Security Update for Microsoft .NET Framework, Version 1.1 Service Pack 1 (KB929729)
Installation status: Failed
Error details: Code 643
Update type: Important
Please does anyone know how to fix this? its been doing my head in!
Thanks,
joby866

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