Edit File: theme-install.php
<?php /** * Install theme network administration panel. * * @package WordPress * @subpackage Multisite * @since 3.1.0 */ if ( isset( $_GET['tab'] ) && ( 'theme-information' === $_GET['tab'] ) ) { define( 'IFRAME_REQUEST', true ); } /** Load WordPress Administration Bootstrap */ require_once __DIR__ . '/admin.php'; require ABSPATH . 'wp-admin/theme-install.php';