That sounds very strange.
First of all, make sure all your users belong only to the "General" group.
If you dont' want to manually do this, go to your database administration console and fetch all records from jforum_groups, and then match the group ids to the records of jforum_user_groups.
I would recommend either set again the permissions for all groups, and restart
Tomcat, just to make sure there is no cached data left.
Btw, which JForum version and database are you using?
Rafael
[originally posted on jforum.net by Rafael Steil]