Error E7D4000C: "This device or media failed to mount 421"

I am trying to back up my new Vista Ultimate using Ghost 14 (both Vista and Ghost new out of the box; never seen the intenet).  I'm trying to back up to the DVD with the image verified.  I've done this twice now and both times it has failed; once when writing the 2nd DVD and once when it was verifing the image on the 2nd DVD (DVD 2 of 2). 

 

The error I get is Error E7D4000C: "This device or media failed to mount 421"

 

What is causing this?   BTW, I tried a third time and backed up Vista  up to a separation partition on the hard drive and it appeared to work fine.  I haven't tried to restore the image but Ghost said its image is fine.