, but there must be a reason why I can unenrol Sean, but not others? 
I've just had a look at the Participants page of the Moodle Tutorial Project and noticed that I can unenrol Sean Keogh or log in as him, but I can't do that with other co-teachers. I haven't unenrolled him, because we beardies should stick together , but there must be a reason why I can unenrol Sean, but not others?
, but there must be a reason why I can unenrol Sean, but not others?
Perhaps because the others have admin/course creator privileges, whereas you and Sean don't have such privileges?
It's just because he was also a student, and thus fair game. 
Boot!
eek! A conspiracy to get rid of me! 