I've never had this issue until today. I'm using version 1.3.5 on a WordPress 2.8.2 site. When I attempt to insert a gallery into the post, the pop up box that allows you to insert the gallery doesn't have the "insert" tab - there's nothing there at all.
As I said, this is the first time I've had problems. Any thoughts? Not a pop-up blocker issue. I'm using FireFox 3.5 BTW.