The plugin documentation says “In most cases where this happens, it is a result of your theme not using the internal WordPress jQuery libraries, resulting in an error when we try to use them. Your theme should be using the same version of jQuery as WordPress. Read Marcus’ post about themes overriding the default jQuery libraries for more information on fixing your theme.”
The article it references is:
I’ve attempted their fixes with no results. I attached a screenshot of what it looks like. The page in question is only available to logged in members, but I’ve created a user profile with permissions to create events for you. Login info to follow.
I’ve also published a help topic for members about creating events. You can view it to navigate to the page with the date picker: