I agree with spinner, if slowing the burn speed (Corny's suggestion) and cleaning the lens doesn't work you might need a new drive. The other Verbs that burnt ok in the past were they the same media ID i.e.
?
Find one of the older ones and pop that in your drive and see if they are the same - it could be your drive doesn't like these discs if they differ to the ones that burnt ok ! In which case you would have to wait and see if a firmware update is available in the future (you are using the most current now) to fix it.