“SYMPTOMS
You cannot gain access to the Windows Update Web site. The Windows Update.log file may contain the following error messages:

Error IUCTL Digital Signatures on file C:\Program Files\WindowsUpdate\V4\iuident.cab are not trusted (Error 0×800B0003: 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 0×800B0004: The subject is not trusted for the specified action.)
CAUSE
This error may occur if your computer cannot connect to a component of the Windows Update site.
RESOLUTION
To resolve this issue, use one or more of the following methods, in the order that they are presented:” See the article.