I had lots of problems with mine at first also. But it seems ok now.
I've used various dvd-rw and dvd+rw media - TDK and Memorex (Ricoh) in mine.
I've also used TDK 16x +r (CMC) with no problems.
Do you have smartburn installed and setup correctly?
I ask because I found the setup screen misleading and had things wrong originally, I believe. There is another thread in here which points you to a slightly newer "test" version which is clearer.
You might also double-check your sata cable and connections to the drive.
Those are the things I played around with to get mine working correctly.