Ive fixed this issue before. The steps are kinda long but they work.
This is for windows computers with iPod nano that get the error 13019 during or after a sync with iTunes.
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-Open itunes
--click, edit, click preferences
--select advanced
---make a note of the iTunes media folder location on a notepad.
---put a check in organize files
---take the check out of copy files
---click ok
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--Click file, at the top of iTunes
--move mouse over library, select organize, and consolidate files. ( This ensures all music in you iTunes will be in the iTunes media folder later.)
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At this point, if you have playlists you want to save:
-Create a folder on your desktop, call it, playlists
--Hover you mouse over your playlist in iTunes, should be at the bottom of the blue/grey column on the left.
--right click the playlist, select export playlist
--Navigate to your desktop and open the playlist folder and save.
---Do this for each playlist you want to save
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-Close itunes
-Click your start button, and open computer or my computer
--Using what you wrote down on your note pad, follow the path to the "iTunes folder", NOT the iTunes media folder
--Open the iTunes folder.
--Stop here
-You will see icons that look like folders and you will see icons that look like files-
-You will KEEP the FOLDERS
-You will DELETE the FILES
--If it makes you more comfortable you can cut the files out and paste on your desktop, but as of now we do not need the files any longer as we have the playlists backed up. Remember-Keep the folders.
--That was the magic--
-Disconnect your iPod if connected.
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-When you open your iTunes, it will be empty, that is OK. We are recreating the library. Everything will come back in a few seconds.
-Click file at the top
--Select, add FOLDER to library, not to be confused with add file.
--In the window that pops up, locate and click on computer or my computer
--From here follow the path to the iTunes media folder on your note pad, but do not open the iTunes media folder.
--Click the iTunes music/media folder one time so it highlights.
--On the bottom right you will have option to select folder, or choose folder or OK. Hit that button.
All you music will start to import back into iTunes.
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-Plug in iPod after completed
--a message pops up about being synced with a different library.
--Click erase and sync
--Watch all your songs go on your iPod with no error message.
From here you may sync your iPod the way you want with out worrying about the persnickety error 13019!!!!!
Hope this helps!!!
Julian
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p.s. Follow the directions exactly.