Drop down menu not working on inserting gallery

I am having this problem: when I try to insert a gallery into a post, the menu loads fine, but when I try to select the gallery, as soon as I click on the drop down manu, a wheel like it’s loading appears but nothing loads. i can not insert galleries, and I need this to be working. Is there any solution??

http://wordpress.org/extend/plugins/nextgen-gallery/