After my Sony DW-P50A refused to write RW's and was replaced after a costumer-service hell, with a whimsical Toshiba SD-R6252 that sometimes wouldn't even read original DVD movies, I went on, spent $110 and got myself a brand new NEC ND-6500A.
I hoped that that'd end the trouble - but after two first (successful) test burns, everything I burn now seems to to be useless. Writing finishes flawlessly, producing a disc which fails miserably on verification. I tried different media (MCC 03RG20, Ritek R04, Optodisc +RW) at different speeds, with identical results.
WinXP SP2, 512MB RAM; Secondary Master, UDMA on.
P.S. When I first installed the drive, the door didn't want to open; I had to slightly loosen the screw closest to the eject button.