You can not select a user to assign to, list is empty.
However, there are 2 blank options, and if you select the 2nd option you get an error: Database Error
In order for users to be displayed in the Assign to field, you have to set them as a manager in the AdminCP.
OK, but this should still be more graceful.
Right now it shows @<option value="0"></option>
When there is no manager set, and selecting the 2nd option causes the above mysql error. Only the option of value="0" should exist.
Fixed, projects now require at least one manager.