I found some discussion of this issue on some online forums, and it seems there a couple of things to look at.

1.) Make sure you are using the correct medium. It looks like users have had problems with certain kinds of DVDs. Make sure you are using a DVD-R or -RW (not DVD+R or +RW).

2.) OR, yes, your rendering could be a problem. Although the error message sounds like it has more to do with the media, the discussion boards mentioned the issue of "buffer underrun" being a problem. If another application is using a lot of processing power while the burn is happening (a render is pretty labor-intensive for your machine; Web surfing is not), the burn application can't get data off your hard drive fast enough for burn.

Trying to burn a DVD with no other applications running might be the easiest (and cheapest) thing to try first.

Good luck!

These were the discussion boards I visited:

http://boards.support.roxio.com/roxio/board/message?board.id=0000020&message.id=13588

http://www.macfixitforums.com/php/showflat.php?Board=Forum39&Number=622725

http://www.videohelp.com/forum/archive/t187815.html