I went to upgrade the new install, it got partway through, then I got this:

 

Fatal error: Access to undeclared static property: IPS\Theme::$defaultThemeSet in/home/mythandm/public_html/init.php(435) : eval()'d code on line 26

 

Now, I cannot access the Admin CP at all, and am stuck. Please help!

Submit a critical ticket.

I submitted a support ticket just now, but no idea where I can mark it "critical". I don't think I have that option, unless I'm oblivious and missing it.

There's an option on submit form. You should check it if your board is inactive due to an issue.

4 hours ago, Ciel! said:

I submitted a support ticket just now, but no idea where I can mark it "critical". I don't think I have that option, unless I'm oblivious and missing it.

This was resolved via a ticket and was due to a third party plugin. 

THANK YOU to IPS for fixing!

 

PS to the rest though - I do not have that "severe client issue" option when submitting my tickets.