Are you sure Sonic burn now can handle RW disks? Perhaps it doesn't have the ability to erase disks! You may need to have a specific dvd burner app for that. Sonic ... is a bundle of tricks, but perhaps its skills in burning & erasing are not as good as a regular disk burner app.

On my comp I have several apps that can erase disks. So if I had a problem with one app, I'd swap over to another.

DVD's are great for mp3's! They can fit just 'SO Much' music! And plus if the files are organised properly is a charm to use on a dvd player.