I recently installed the newest Pioneer DL burner as well. After no luck at all burning DL+R media I did much research and got advice from several folks who basically said, “DVDA is great for authoring, but not so great for burning”.
I purchased RecordNow Deluxe 7.3 for $30 and haven’t had a single problem burning DL since. Just prepare the project to a folder, drag and drop the files onto RecordNow and click burn.
(Maybe Sony should just bundle RecordNow or Nero with DVDA).