Marketpress problem

Hi, I just bought Marketpress and when I click on Store settings in admin menu it says "Fatal error: Call to undefined method stdClass::add_help_tab() in /homez.318/dextera/www/wp-content/plugins/marketpress/marketpress.php on line 594".

Also, I didn't find any information on how to actually use the plugin in themes, is there such a page?

Thank you

Vitaly Kolesnik