I checked the paths in the main.inc.php, and they are set correctly. (I have them both set to the same path, since I've not moved my config..yet
The permissions are the same as before I upgraded. I can reupload my old files and it starts working again.
I don't know if it makes any difference or not, but the only difference between the test server and the main server is that the main server has multiple categories with specified stylesheets, headers and footers.