Hey @David,
This is unfortunately a known bug that we have just fixed. Stay tuned to the official release of version 4.0.1, coming very soon – you should see an update notice for it, and then updating should fix the problem.
—
If you would not like to wait, then you can get the files now and manually update them on your site. Do not do this unless you know exactly what to do!
But if you want to do that and can perform the manual installation fine, you can get files for the 4.0.1 Release Candidate here → http://theeventscalendar.com/my-account/downloads.
Cheers,
George