User Accounts> List Users ->
The "Open Panel Icon" for each user is directing the link to the IP of the user panel instead of the hostname thereby causing an SSL certificate mismatch as the panel is secured using the actual hostname. One can add an exception to some browsers, but the "Open Panel" icon should really use the hostname. The account details when you create a user refer you to the hostname address for access to the panel. I would think this would be an easy fix, just read the hostname from the db rather than the IP.