The problem was when you register, warnning, "ID already in use" popped up although it was the first try.
The problem is solved now.
The student who faced this message was registered with the info at the first try.
And if you want, you can modify your info any time.through "Modify profile info" menu
p.s Student ID means "Hak-bun(학번)" Therefore, the students who have already register with other id than 학번 should register again. In a few days, not student id will be erased.
Students should use student id because you are not a guest!