Membership error- not able to access anything

I updated the plugin last night. After doing so my membership site was no longer accessible to anyone. The error that is showing across the top of the site is:

Warning: Missing argument 2 for wpdb::prepare(), called in /home/content/44/8609544/html/wp-content/plugins/membership/membershipincludes/classes/membershippublic.php on line 2312 and defined in /home/content/44/8609544/html/wp-includes/wp-db.php on line 990

Warning: Missing argument 2 for wpdb::prepare(), called in /home/content/44/8609544/html/wp-content/plugins/membership/membershipincludes/classes/membershippublic.php on line 2312 and defined in /home/content/44/8609544/html/wp-includes/wp-db.php on line 990

I am not an developer so please explain how to fix this in very simple terms. I am loosing lots of money as I have a major add running today!!! I need to fix this asap, any help would be very appreciated.

Thanks-- Kim