Thread:Project:Support desk/can't find CSS after upgrade from 1.15 to 1.20/reply (2)

What Vulpix says nicely shows your actual problem: Between MediaWiki 1.15 and 1.18 a new file called "load.php" has been added to MediaWiki. This file is responsible for loading the skin. However, in your case this does not happen, because of the redirect (which should not be there): Currently on your server, calls to load.php are rewritten to the main index.php script. In most cases this wrong redirect is caused by one of the rewrite rules in .htaccess.

Change your .htaccess file to make sure that calls to load.php (and to api.php btw.) are not rewritten and the right contents should be displayed:

RewriteEngine On RewriteRule ^(api|load)\.php - [L] ...