[AAR.oner]

i've had a lot of problems burning DVD9 discs in the past...assuming yer burner is a dual layer burner, it could be that yer drive doesn't like the brand of discs...also, apple usually uses Matchita drives in their comps, which are complete shite imo...i've had 2 drives die within a year [won't burn anything, only reads certain discs]

try another burning utility like daddyrayoll mentioned [Burn should be just as good as Toast]