Use pmpro_getfile_before_error to tell PMPro to do something else besides send a 503 when accessing a member file. Requires PMPro 1.7.15+

my_pmpro_getfile_before_error.php

/*
	Redirect to the levels page when users try to access protected files in PMPro.
	
	Add this code to a custom plugin or your active theme's functions.php file.
	
	Learn about protecting files with PMPro here:
	http://www.paidmembershipspro.com/locking-down-protecting-files-with-pmpro/
*/
function my_pmpro_getfile_before_error($filename)
{
	wp_redirect(pmpro_url('levels'));
	exit;	//need to exit at end of function to avoid sending the 503
}
add_action('pmpro_getfile_before_error', 'my_pmpro_getfile_before_error');