Can't activate the plugin

I’m was trying to customize the rating plugin from the power user customization option, but suddently the plugin stopped working, then I had to reset the plugin to the default options and after that, the plugin started to ask for registration again, and when I try to register to activate it, it shows me this error;

Warning: Attempt to assign property of non-object in /homepages/3/d385375234/htdocs/coverest/beta/wp-content/plugins/rating-widget/rating-widget.php on line 680

Warning: Attempt to assign property of non-object in /homepages/3/d385375234/htdocs/coverest/beta/wp-content/plugins/rating-widget/rating-widget.php on line 680

Warning: Attempt to assign property of non-object in /homepages/3/d385375234/htdocs/coverest/beta/wp-content/plugins/rating-widget/rating-widget.php on line 680

I already had deactivate and deleted all other plugins and deleted and re-downloaded the rating-widget plugin again, also i used the twenty-twelve plugin to test, but the error still there.

https://www.ads-software.com/plugins/rating-widget/