Undefined property

When one attempts to purchase a product on our site, the paypal never stops spinning around an an Error message is returned.

I am receiving an Error Message:

Notice: Undefined property: stdClass::$slug in /hermes/walnaweb09a/b1319/pow.yarlungrecords/htdocs/yarlungrecords-site/wp-admin/includes/class-wp-plugin-install-list-table.php on line 52

I am not able to complete a Transaction.