Site crashed when changing global cart settings

Hi,
I went to change my network settings to Global Shopping Cart to see what options were available to me in regards to payment options. After I checked it I got a fatal error. Now I can't even get back in to my dashboard to do anything!
Fatal error: Cannot use string offset as an array in /home/mylocalc/public_html/wp-content/plugins/marketpress/marketpress-includes/marketpress-ms.php on line 220

If you try to look at my website you just get this.
Fatal error: Cannot use string offset as an array in /home/mylocalc/public_html/wp-content/plugins/marketpress/marketpress-includes/marketpress-ms.php on line 220

Help!