How to block posts in parent forum but allow in sub forums?

[RateU]

If you want to use it as a category (nobody can post in it, including administrator), set the parent forum as category, not as forum.

But, if you want some usergroups to be able to post threads in the parent forum, you need to set the parent forum permission.

EDIT:
Oooops... I'm sorry, x-Treme
The same time hitting the post reply button