The Windows Update log file, either:
Error IUCTL Digital Signatures on file C:\Program Files\WindowsUpdate\V4\iuident.cab are not trusted (Error 0x800B0003: The form specified for the subject is not one supported or known by the specified trust provider.)
Error IUCTL Digital Signatures on file C:\Program Files\WindowsUpdate\V4\iuident.cab are not trusted (Error 0x800B0004: The subject is not trusted for the specified action.)
To resolve this behavior:
1. Make sure you are running the most current version of Internet Explorer. If updating Internet Explorer resolved this issue, exit this procedure.
2. If you are using a proxy server, have the network administrator verify that the proxy server allows anonymous connections to the Internet.
3. If you are using a proxy server, on the Internet Explorer Tools menu, press Internet Options and select the Advanced tab. The Use HTTP 1.1 through Proxy Connections box should be checked. If the problem is resolved, exit this procedure.
4. Open a CMD.EXE window.
5. Type the following commands, pressing Enter after each one, and pressing OK when you receive the the DllRegisterServer succeeded message:
If the problem is resolved, exit this procedure.
6. Verify that the Hosts file at %SystemRoot%\system32\drivers\etc does NOT contain any entry for Windows Update. Some third party applications may add a static IP entry for Windows Update.