Why doesn’t Windows Update work IE 6?

I have a few computers that are having a problem with Windows Update. I am able to access the Windows Update website, and everything works until I get to ‘Install Now’. I click on ‘Install Now’ and the dialog box pops up ready to download the updates. The problem is it stops, and nothing downloads or installs. I cancel and I get the following message to be sent to Microsoft.

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Error details
Internet Explorer has encountered an internal error.
Error signature
AppName: iexplorer.exe AppVer: 5.51.4801.2300 ModName: rpcrt4.dll ModVer: 4.71.2900.2 Offset: 00040894

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This problem is on computers that has had IE 6 installed, and run on a Windows 98 OS.