Wordpress error in WYSIWYG editor. The load of post.php produces a “tinyMCE is undefined error” Resolve: In file /wp-includes/js/tinymce/tiny_mce_gzip.php search function_exists('ob_gzhandler') && !ini_get('zlib.output_compression')) { and change with: function_exists('ob_gzhandler') && !ini_get('zlib.output_compression') && get_settings('gzipcompression')) { save file, clear browser cache, reload wordpress editor. DONE. (ByREV)