Ok I tried using Erase first, but it wouldn't do that either, still asked me to insert a blank disc.
So I brought up Nero instead and used the Erase function. Nero was able to erase the disc. Great, I thought.
Now I go back to Alcohol, try to burn the image and it says...
"Not an empty disc"
Really! I just erased it and it is complaining that it's not empty? Does Alcohol even support DVD+RW?