New Post: "(50,8):Command:" Exception triggered on OK for Task Editor

First, thanks for all the work you've done on this very nice library! I allows me to edit and monitor existing tasks very nicely.
I bumped into a problem with creating a new task. A click on the OK button triggers a "(50,8):Command:" exception. See image with more detail here: http://screencast.com/t/k98w6BiKDwz3

editorForm.RegisterTaskOnAccept is set to True.

Any idea what could be causing this exception?