Even if that's not the specific cause, the following posts should give you enough of a headstart to figure out the permissioning problem...

http://openacs.org/forums/message-view?message_id=62729
http://openacs.org/forums/message-view?message_id=69588

And there's a bug entry that references this particular issue that indicates that it's a *bug* to have the capability to do this from the UI:

http://openacs.org/bugtracker/openacs/bug?bug%5fnumber=39