The thing’s that it also happens on IE7. I think it could be that thickbox.js is “repeated” (because it is in wp-includes/js/thickbox) and on the nextgen-gallery folder. I also have some little problems (like in some browsers is shown an image for closing, because the original thickbox comes with that, and in other browsers is shown the original text of next-gen that says “close (esc)”) and things like that.
I’ve had tons of problems because of this duplicated issue, how can this be fixed? Is there any problem having 2 thickboxes?