Problem to assign membership

Having problem assigning memberships to any user.

I'm getting the messages:

Warning: Creating default object from empty value in C:\wamp64\www\bitfarm\wp-content\plugins\membership\app\controller\class-ms-controller-member.php on line 401
Fatal error: Call to undefined method stdClass::save() in C:\wamp64\www\bitfarm\wp-content\plugins\membership\app\controller\class-ms-controller-member.php on line 404