today i have updated October CMS and from than i getting this error

Cannot access protected property Backend\Widgets\Form::$allFields plugins\benfreke\menumanager\controllers\Menus.php line 84

any solution ????

The plugin needs to use getFields() accessor instead.

Yeah, this commit broke it: https://github.com/octobercms/october/commit/f99bd0e427e43fa5d43a266fd2de6cc6b67bb37c

You need to wait for BenFreke to update his plugin ;)