DL DVD-R fail to burn - Spindle Servo Failure

Got a frustrating problem with my new Mac Pro - the super drive will not burn DVD-DL, + or -. I am always receiving a Spindle Servo Failure when writing the lead out.... I've tried burning with Verbatim, Ritek and Memorex, and they all fail the same way.

I've tried writing using DVD Studio Pro, Finder, and Toast 9, and get the same error every time (also slowed the burning to 2x). Should I assume hardware failure at this point?

Thanks in advance!

Robin