Error when adjusting Member Level!

I'm setting up Membership on a test site for the first time, and I went through the signup process myself (while still signed in as superadmin on my WP Multisite install...oops?) just to see what it looked like, and I made myself a "reader," which is my initial subscription level for folks that sign up.

But I went to move myself to the next level up, "Author," and I got this error at the top of my screen, and the change does not appear to have taken effect:

Warning: Missing argument 2 for wpdb::prepare(), called in /home/*****/public_html/wp-content/plugins/membership/membershipincludes/classes/class.membership.php on line 447 and defined in /home/*****/public_html/wp-includes/wp-db.php on line 990

Warning: Missing argument 2 for wpdb::prepare(), called in /home/*****/public_html/wp-content/plugins/membership/membershipincludes/classes/class.membership.php on line 447 and defined in /home/*****/public_html/wp-includes/wp-db.php on line 990

Warning: Cannot modify header information - headers already sent by (output started at /home/*****/public_html/wp-includes/wp-db.php:990) in /home/*****/public_html/wp-includes/pluggable.php on line 876

Warning: Cannot modify header information - headers already sent by (output started at /home/*****/public_html/wp-includes/wp-db.php:990) in /home/*****/public_html/wp-includes/option.php on line 568

Warning: Cannot modify header information - headers already sent by (output started at /home/*****/public_html/wp-includes/wp-db.php:990) in /home/*****/public_html/wp-includes/option.php on line 569

What can I do to remedy this?