Grrr... my computer has been attempting to download this particular update for days and it just fails each time.

Refrence link: http://answers.microsoft.com/en-us/windows/forum/windows_other-windows_update/updating-window-error-code-windowsupdate00000643/b73f3afa-5d72-403e-ab85-363f91b27e8c To troubleshoot this problem, follow these steps starting with Method 1. Proceed to the Method 2 if Method 1 does not resolve the problem. Method 1: Fix MSI software update registration corruption issues <script type="text/javascript">// <![CDATA[ loadTOCNode(3, 'resolution'); ]]></script> For more information about how to fix MSI software update registration corruption issues, click the following article number to view the article in the Microsoft Knowledge Base: 971187 (http://support.microsoft.com/kb/971187/ ) How to fix MSI software update registration corruption issues To fix this problem automatically, click the Fix it button or link in the 971187 article. Then visit the Windows Update Web site and try to install the updates: http://windowsupdate.microsoft.com (http://windowsupdate.microsoft.com) If the problem is not resolved, proceed to Method 2. Method 2: Repair the .NET Framework <script type="text/javascript">// <![CDATA[ loadTOCNode(3, 'resolution'); ]]></script> To repair the .NET Framework, you must uninstall multiple versions of the .NET Framework by using the .NET Framework Cleanup Tool, and then reinstall the components. To do this, follow these steps: Click the following link to download the .NET Framework Cleanup Tool: http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx (http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx) Use the .NET Framework Cleanup Tool to uninstall the .NET Framework versions 1.0, 1.1, 2.0, 3.0, and 3.5 Note The cleanup tool does not let you remove the .NET Framework 2.0 in Windows Vista or later versions because the .NET Framework is installed as an operating system component. Restart the computer. Download and install the following components: .Net Framework 1.1 http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3 (http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3) .Net Framework 1.1 SP1 http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en (http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en) .NET Framework 3.5 SP1 Note This will also install .Net Framework 2.0 SP2 and .Net Framework 3.0 SP2 http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en (http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en) Restart the computer. Visit the Windows Update Web site and install the updates: http://windowsupdate.microsoft.com (http://windowsupdate.microsoft.com) Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. ”