Unable to checkout using Paypal Express

Okay, I've been using this plugin for a while and have just recently been getting a "Whoops, looks like you skipped a step! Please go back and try again." error. I started with the lite version of the plugin, needed some additional features and upgraded to the paid. The paid version has been in use for a week and this error showed up today.

There hasn't been a change to the server, Wordpress, or any other plugins. What can I do to get this fixed?