The problem:

This problem might be caused by some faulty or outdated plugin .js that overrides something else when it is concatenated.

Open and edit the wp-config.php file (located on the root folder of the installation ). Make a backup of wp-config.php first.

add this define('CONCATENATE_SCRIPTS', false);

right before the line of: /* That's all, stop editing! Happy blogging. */


This will tell WordPress to load each script on it’s own instead of combining them.