XF 1.5 "You must select forum" Error


I've recently been moving some nodes around on my forum page, and one of the staff just noticed that with some of the forums, you cant actually make any posts. When you press "submit", it gives you an error saying:

"THE FOLLOWING ERROR OCCURRED: You must select forum."


XenForo moderator
Staff member
How did you move the nodes around?

Do you have any add-ons installed?
Does the error still occur with all add-ons disabled?