Category problem

Hey.

On my site when someone is posting an add they see 2 boxes where for category.. one with all the categories and 1 you can blank.. this is where you can add the categories to.

It use to be just a drop down and you can select 1 category.. How do i get this back to the drop down ? .. I don’t want people being able to add there ad to every category on the site..

All my listing packages where set to 1 category.. but it didn’t limit you to 1.. so i set it to 0 but it’s still not limiting people.

Is there a different area I need to change ?

thanks.