Thread:Project:Support desk/Fatal error: Class 'MonoBookTemplate' not found in.../reply (10)

Alright, the folders with their names all in lowercase come from older versions of MediaWiki. These folders should have been removed during the upgrade to 1.24. You should remove them. Also, if you still have files (e.g. called Vector.php, Modern.php and so on) directly in the skins/ folder, meaning outside of the according Vector/ and MonoBook/ folders, remove these files as well.

Make sure that you have a require_once line for the Modern skin in your LocalSettings.php file like so:

require_once "$IP/skins/Modern/Modern.php";

Add according lines for all skins, which your visitors should be able to choose from (or which they might be using already). Without such a line, a user, who is using the according skin, will get a fatal error.

If that does not solve the problem, then it will at least improve the situation.