Hi Tom,
thanks for your reply. I packaged the plugin with a theme. And u were right. The paths to the javascript were the problem.
I solved it by setting the path-variables to:
define( 'MEGAMENU_VERSION', $this->version );
define( 'MEGAMENU_BASE_URL', trailingslashit(get_template_directory_uri() . '/inc/plugins/megamenu') );
define( 'MEGAMENU_PATH', get_template_directory() . '/inc/plugins/megamenu/' );
For evrybody else reading this: You also have to change the init-hook to:
add_action( 'after_setup_theme', array( 'Mega_Menu', 'init' ), 10 );