I am having the same issue as a user that posted earlier (different line #):
Warning: get_class() expects parameter 1 to be object, string given in
wp-content/plugins/restrict-widgets/restrict-widgets.php on line 218
...to which you replied that the get_class() function doesn't even exist in your plugin. Well, yes, it does. And it's causing problems. Don't know if it's been added since the other user posted (3 months ago) but I've had to use another widget control plugin for now.