Apple – Support – Discussions – iPhone 4 iTunes Unknown Sync Error 13019 ….  Two ways to fix this.

1. Delete voice memos.
2. I also experienced this error, but didn’t want to delete my voice memos so went this route:

(1) opened iTunes
(2) clicked Music
(3) searched for Voice Memos
(4) right-clicked on one Voice Memo and chose Show in Finder
(5) right-clicked my Voice Memos folder (in Finder) and chose “compress” to make backup
(6) back in iTunes, I re-ordered my Voice Memos by length… with the idea that the same length ones might be duplicats… then played same-length ones back-to-back to make sure they were duplicates and deleted the 2nd (or sometimes more) duplicated file

Of course then (after!) I found the following command in iTunes that can probably more reliably display dups, and you may be able to delete by playing back-to-back to confirm:

(7) chose FILE/DISPLAY DUPLICATES (Thanks krisvannest)