ImgBurn sends the set layerbreak command and then checks if it was correctly set, to which the burner answered OK: after this it depends entirely on the burner, its firmware and media support. The problem is that the blanks you're using are crap. Also notice that the booktype wasn't set to DVD-ROM, which not only ImgBurn does by default on Samsung burners, but the burner itself also does it.
Update your burner's firmware and try burning at 6x or 8x. If that doesn't help then read this -> http://forum.imgburn.com/index.php?showtopic=8000