Did you recently update/upgrade your Moodle to 3.7.2?
Reason asked ... compatible themes are now boost based. I see in the debug many references to older themes in caches.
What is your default theme?
To clear things up would recommend manually removing contents of ... that's contents of ... moodledata/cache and moodledata/localcache
as well as adding this line to config.php:
$CFG->theme='boost';
or 'classic' ... those are the themes for 3.7.x now.
Once you gain access again to admin of the moodle and you want to find another theme to install, make sure they are 3.7.x compatible.
Set default theme.
Then comment out the theme line you added to config.php by putting // in front.
'SoS', Ken