If you want to edit your Joomla menu from admin and when you see and error
Fatal error: Cannot use object of type stdClass as array …your site path /plugins/system/helix3/helix3.php on line 55
you need to update your both plugins helix.
so, make full backup and download template zip from
plugins/zip both and you will have ajax.zip and system.zip
Install both and clean cache after.