Single Event Item menu not working (blank pop-up on Select Event)

I'm using the awesome ES 1.3.3 on Joomla 3.3.

I've got 2 created events. I want to set up a menu item for one of them. I go to 'New Menu Item' back-end and then 'Single Event Item'.... when I then click the 'Select Event' button, I just get a blank pop-up appear.

Can't get beyond that.
Can you replicate that bug? (I'll be back to add my site details shortly)