Medium Write Error

Hi All, My new Mac Pro, which has been humming along beautifully for months now, is suddenly giving me the following error:
Burn error ox8002006E The burn failed because of a medium write error
I have tried 2 different brands of dvds and an old project that burned successfully a few weeks ago. Pretty much consistantly the same error. Once the old project burned successfully but wouldn't play.
So....software or hardware problem?
I am thinking of updating DVDSP, but not sure if I have to do the whole suite so they play well together. Will I need to update QT and how will that affect FCP?
Thanx Barry
Mac Pro, dual quad 2.6ghz, 4 gigs ram
FCS2, DVDDP 4.2.1

What brands of DVDs ? ... and have you tried just building of the DVD (into a folder) and then using DiskUtility to burn the DVD separately. Just shooting in the dark here as I use Toast