Sorry, very busy at mo and this only comes through to my laptop…
I’ll have a proper look at the weekend, however a quick Google and it looks like that warning can be ignored, its a mismatch in your server certificates or “httpd.conf”. This shouldn’t be an issue for a theme, that said, if its somehow redirecting then the links in WordPress may be different and what is causing the problem.
I believe that warning may be a host issue (if you haven’t played with https, certs, etc) concerning HTTPD (Apache), this was the best I found on this quick search:
https://www.entrust.net/knowledge-base/technote.cfm?tn=6559
I’m no expert with WP, but am intending to make my own theme, so will be glad to look into it to help bring me up to speed with possible issues…
*** I changed some things the other day in a theme and wasn’t able to access the dashboard either, deleting the theme directory and revisiting the dashboard put things back to normal. This’ll hopefully allow you to keep on managing your site, but just without the new theme…