So it is official, the column classes were purposefully removed from v2.3.0 of the base Genesis Framework theme. That being said, nearly all child themes still use these classes so the majority of users should have no issue.
If you are using the base Genesis Framework as the theme of your site, StudioPress now advises that this should never be done and you should always be running a child theme as well. You will probably see a notification about this in your WordPress admin if you upgraded to v2.3.0 and are just using the base theme.
The best course of action in this case it to install the free Genesis Sample Theme. It has been completely rebuilt for v2.3.0 and contains the column classes you need for this plugin. You can download it from GitHub here (https://github.com/copyblogger/genesis-sample). Click the green button on the right.
As an aside, I am hard at work on version 2.0 for this plugin. In light of the column classes being removed from Genesis v2.3.0, I adding an option in version 2 that allows the plugin itself to serve the required CSS. This will allow the plugin to stand alone from Genesis.
Again, I apologize for the inconvenience. If you are running the base parent theme, I highly recommend you upgrade to the free Genesis Sample Theme. Also stay on the lookout for version 2.0 of this plugin coming next week.
Thanks,
Nick