I don't know if you are going to get much help here on the forum's, so would suggest you open a GTAC ticket for this (you are likely to get a faster resolution). it sounds like a certificate has expired, if you are redirecting users to a webpage, then id try going there directly from a computer and see if you get the same error. Plus you can view the certificate details in any browser which will help you see what's going on.
-Jason.
