I recently installed 2013 in my 2007 environment. I moved over one mailbox and opened Outlook and everything seemed to work fine. I then installed a new UCC from GoDaddy and migrated the other mailboxes. After all completed, I tested Outlook 2007 again and now get this every time.
So is it something with the certificate or am I missing something?.?.? OWA works fine and I'm able to log in w/o issue there.