I'm having the same problem updating the following:
Microsoft .NET Framework 1.1 Service Pack 1
Installation date: 12/16/2007 3:04 AM
Installation status: Failed
Error details: Code E0434F4D
Update type: Important
Microsoft .NET Framework 1.1 Service Pack 1 resolves various issues found after the initial release of .NET Framework 1.1. These include both security- and non-security-related issues. After you install this item, you may have to restart your computer. Once you have installed this item, it cannot be removed.
More information: http://support.microsoft.com/?kbid=867460
Help and Support: http://support.microsoft.com/?kbid=867460
The links have not been very helpful at all.
Any ideas why this would fail?