I'm not sure, I am in the exact same situation. I have DR-M10 and the DVD drive won't read RW disks.
I have tried a Dual Layer DVD burner from my PC but it won't accept it. I then tried a DVD-ROM drive and this worked.
I'm assuming my DVD-RW was too new for the DR-M10. So I am going to try an older DVD-RW drive from a freinds machine.
Neil White, May 2008