I have been asked to update this site http://dynamictherapies.net
Background situation— The theme is a heavily customized Eximius theme, which may have been purged from the listings because it is not being kept updated. This site customized the theme heavily, but without turning it into a child theme. It is backed up by iDrive, a plugin no longer supported, so I want to pursue all alternatives before resorting to installing the backup. (A new backup method was at the top of the list, to be followed by WordPress!)
The problem— Most of the Admin panel is inaccessible. It opens into the media library, but all other links yield:
Fatal error: Call to undefined function get_current_screen() in /home/dynamict/public_html/wp-content/plugins/all-in-one-seo-pack/aioseop_module_class.php on line 612
Since I am unable to access the plugins page I can't disable All in One SEO Pack. I have to jump through some hoops to get FTP access, and I'm not at all confident that just removing the plugin wouldn't risk compounding what is already a bad situation. It is also not clear that this plugin is the root cause. It is quite possible that some of the plugins are updated to run with newer versions of WordPress than what is currently running on the site, but since I can't access the page I can't even say with certainty what those plugins are, much less their versions.
Short of starting to explore the backups, can anyone suggest how I might regain access and do some repairs?