It's possible you may never get the image to burn to a disk. Typically, there needs to be a break in the data so the laser can move from one layer to the other.
If you've ever created video content, more advanced authoring software asks where you want to put the break so xxx files go to layer one, and zzz files go to layer two. So you may put the main movie on layer one along with the menu screen, and all of the other stuff on layer two (behind the scenes and other extras). Ever watched a movie where it fades to black and back in at a point where no such fade out happened in the theatre? Or there's a brief halt in the playback? That's the break put into the video where the laser has to jump. They are two distinct files where one ends, and the other starts.
An .iso file is just one big compressed file. There's nowhere to put a break, and so may be why the burn fails even on a dual layer disk.