It wouldn't work if only Creator (the big multi-menu thing) was running. The only way I could get it to work was to run Roxio Burn, so this box was visible down in the bottom right of the screen.
Then I had to right-click on the ISO and click the flaming disc option
Doing that loaded the ISO into Roxio Burn and I then had to click the flaming disc which appeared on the right end of Roxio Burn.
Seems a great way to complicate what had been a relatively simple process in NXT4?