Theme Customizer does not work

Hi, I recently installed the My Music Band Pro theme and all the required plugins, but when I try to "customize" it either by clicking the "customize" button on the header or by navigating from the dashboard to "appearance -> customize or header or background" I get the following page /wordpress/wp-admin/customize.php: There has been a critical error on this website. Please check your site admin email inbox for instructions. Learn more about troubleshooting WordPress.