Wordpress MU won't create the permalink i want to use


i recently created a page on my blog with the permalink

i deleted this page, and then tried to recreate the page.
the permalink created became http://www.domainname.com/gallery-1

i tried to edit it out, so that it went back to the original http://www.domainname.com/gallery.
but no luck, when i try and publish it, it goes back to the gallery-1 format.

i deleted again, and tried to recreate again, and this time i get gallery-2 format.

I'm guessing that somewhere in wordpress it has registered that this permalink has been used before, adn won't let me use it again, i'm just wondering how can i reset this, so i can create the permalink i want to use: ie http://www.domainname.com/gallery?