I recently upgraded to WordPress 3.5 and discovered the Add Media button in Posts doesn't work when HTML5 jQuery Audio Player (Pro) is active. Disabling the plugin will restore the Add Media Button functionality.
I also noticed that the plugin causes the WordPress submenus to stop working. Normally when you mouse over the admin menu, there is a fly out submenu for additional items. When the audio player plugin is active, the submenu, will not show.
In researching the issue, I discovered there were similar conflicts with other plugins related to the Add Media button. The suggested remedy was to add the following to wp-config.php:
define('CONCATENATE_SCRIPTS', false );
This should be added before:
require_once(ABSPATH . 'wp-settings.php');
This corrected the submenu issue, but has not solved the Add Media button problem. Anyone else experiencing issues, and more importantly figured out a solution?