Windows XP "The signature of the certificate can not be verified" (error 0x800960004)

According to this article, it could be an Windows XP problem.

See here:

http://answers.microsoft.com/en-us/ie/forum/ie8-windows_other/the-certificate-in-the-signature-cannot-be/76a1ec7f-02f0-4b74-b7d3-eff3993684ba