User sign-up upon course enrollment displays blank screen

On a Wordpress single site (haven't yet tested multisite) with CoursePress installed, I am able to routinely reproduce a blank modal screen after a user has entered their registration information. That looks like this screenshot:

https://drive.google.com/open?id=0B8DaDY6VuDfET3pnSF9HRWg0aWM&authuser=1

The user's information is successfully registered with the site, and if I close the modal, the user will be both registered and logged in, but I do have to close the modal.