Thanks for the response, Liggy.
That's really wild!
I wonder what it could possibly be not writing on the existing media that would cause it to fail? There must be something different about the first time that a DVD +RW is written to than later rewrites.
I tried a 'full erase' of the disk in another drive which has set the booktype to dvd-rom then tried burning it again in this one and that didn't help.
Guess I have a choice of buying all new 8x dvd +rw media or swapping in one of the old dvd burners.