MarketPress on sub domain

Hi, I have just installed the market press plugin. All was well on my main site, but when I went to check it out on a subdomain I got this error:
Fatal error: Cannot use string offset as an array in /home2/fondelif/public_html/wp-content/plugins/marketpress/marketpress.php on line 342
I have tried the plugin in both the mu-plugins and plugins folders, but have the same result.