Go to Group Chat in Admin Console, then Group Chat Settings > select your conference service, then Room Creation Permissions
Depends on a client. With Spark you can try to control broadcasts (mass messages) with Client Control plugin on a server. But there is no guaranteed way to forbid this completely as user can just send a mass message as a bunch of simple messages. Client Control plugin can disable general broadcast messages, but can’t forbid sending massive messages by selecting a group of users in roster. But i haven’t tested this for a while. You should try this plugin.
I’ve fixed that… There was a problem while the server tried to create the tables of the database… I’ve simply reinstalled it and it worked! Thank you for the tip… =)