[Plugin: WordPress Navigation List Plugin NAVT] :: duplicate name :: problem

Im trying to create a new group but I get the error

:: duplicate name ::

However there is no other group with that name displayed on the screen. In the wp_options table i can see the wpnavt_assets contains this group name, but i dont know from where till where i need to select and delete in order to get rid of this problem, if this is at all the solution. Any help please? thanks!

http://wordpress.org/extend/plugins/wordpress-navigation-list-plugin-navt/