I have a site running EE2.9.0 using Focus labs config set-up.
These are returning 500 Internal Server Errors in the inspector in Chrome. I am getting the same in Firefox.
It is all working fine locally and on a staging server so I guess it's something server related but I'm struggling to pin it down.
I've tried stripping everything out of htaccess but that didn't seem to help. I've also tried various combinations of trailing slashes/no trailing slashes on theme_folder_path and theme_folder_url.