This plugin is bad, and the developers should feel bad.
THe "support" for this software is embarrassing at best. Even having paid for support you can't get anyone to answer emails... ever. Take a look at their forums http://getshopped.org/forums/ you'll find that just about every topic is full of people not getting any help.
The last but won't let people buy things! They posted an update on their blog letting everyone know that the plugin they wrote isn't compatible with the premium add-on THEY WROTE! Once they got around to making a quick patch for the error, no one seems to see it as being resolved and in fact the "fix" let the error continue while introducing new errors.
This is some sad, sad development. Just avoid the plugin. Move on. Save yourself the headache.