The old "inferior standard" ploy. You don't know what the answer is.
I have the first Pioneer DVD burner which burns only -R discs so I know all about -R and +R and from what I read about them, there is no difference in the playback. It's another way to try to confuse the buyer like HD DVD and Blu Ray. Modern burners burn on both. The truth is, the error "cannot set layer break position" is bogus. There must be 20 posts on here about it and Imgburn should remove the error or change the wording to be less draconian.
It works, it's fine, life goes on.