There is a problem with the proxy server's security certificate (internal Outlook 2013 users)

I am receiving the above message for internal Outlook 2013 users when they open Outlook. Despite this message, Outlook is fully functional. External OA users do not see this message. We are using an SRV record for our autodiscover and pointing it to the name on the single cert we have. I've also already changed the outlookprovider record in Exchange. Any ideas?

TIA!