Well, in my experience, dual-layer burning can be fickle business, with a higher fail rate than CD and single-layer burning, so I wouldn't say right off the bat that it's a broken drive.
I had a similar issue a while back, and found that using a different brand of media fixed the issue right away, so I'd suggest you try the same. Incidentally, Verbatim was the brand I actually got to work, whereas Memorex and [brand which I forget] failed repeatedly. Unfortunately, given the relative cost of these sorts of disks, experimentation isn't too cheap.