I am currently working on a new site using the Genesis Framework (in a local environment - MAMP) and as soon as I activate Marketpress, the wp-admin panel breaks (i.e. blank screen, and there is no way to get around this other than deleting plugin from plugins directory in Finder.)
If I enable a different theme, prior to activating MarketPress, it works, until I activate Genesis (or child theme.)
Also, I tried Marketpress Lite and it works just fine!
I am running the latest version of wordpress, and there are NO other plugins activated, or installed.