Invalid argument in plugin.php

Invalid argument supplied for foreach() in wp-admin/includes/plugin.php on line 1290

function remove_menu_page( $menu_slug ) {
	global $menu;

	foreach ( $menu as $i => $item ) {
		if ( $menu_slug == $item[2] ) {
			unset( $menu[$i] );
			return $item;
		}
	}

	return false;
}

line 1290 is foreach ( $menu as $i => $item ) {