Upgrade Marketpress Broke WordPress Menu

When I updated Marketpress it appears to have broken the site. The front page shows up but the Login / WordPress Menu Bar at the top of the screen no longer appears. When I disable the Marketpress plugin it works fine so the issue appears to be with Marketpress.

At the bottom of the page there appears the following error message:

Fatal error: Error! MarketPress doesn’t have a get_cart_contents method. in /home/saleencl/public_html/wp-content/plugins/marketpress/marketpress.php on line 937