Quick answer: Delete the corrupt file from the sync list or from the device, then re-sync. If that doesn't work, check file permissions and device drivers.
What's going on with this error?
This error code 0xC00D1236 pops up when Windows Media Player tries to copy a file to your portable device—phone, MP3 player, whatever—and something in the file or the connection stops it. Usually it's a corrupt media file, a damaged file system on the device, or a permissions issue where Windows can't write to the device. Had a client last month whose entire playlist of 200 songs failed because one MP3 from an old download had a bad ID3 tag. Took me an hour to track it down until I realized it was just that one file.
How to fix it (the steps that actually work)
- Find and remove the bad file
Go to your sync list in Windows Media Player. Look for theSynctab. Right-click each file that shows the error, and choose Remove from list. Then reconnect your device, and try syncing again. If the error's gone, you found the culprit. - Delete the file from the device manually
If the file already synced partially, Windows Media Player might hang on it. Open the device in File Explorer (like a USB drive), find the song or video causing trouble, and delete it. Re-sync. - Check file permissions
Right-click the problem file in Windows. Choose Properties > Security. Make sure your user account has Read and Write access. If not, click Edit and grant full control. This happens a lot with files copied from external drives. - Run Windows Media Player as administrator
Close it, then right-click the shortcut and choose Run as administrator. Try syncing again. Sometimes Windows media services need higher privileges to write to older devices. - Reformat the device (last resort)
If nothing else works, the device's file system might be corrupt. Back up your music to your PC, then reformat the device as FAT32 (most portable devices need this). Re-sync from scratch. Had a client with a 2010 Sandisk Sansa who had to do this—fixed it permanently.
If the main fix doesn't work
Sometimes the device driver is the problem. Open Device Manager (right-click Start > Device Manager). Expand Portable Devices. Find your device, right-click, and choose Update driver > Browse my computer for drivers > Let me pick from a list. Choose the generic MTP USB Device driver. That swaps out any flaky manufacturer driver. Works about half the time.
Also, try a different USB port. USB 3.0 ports have sync issues with older devices. Plug into a USB 2.0 port instead.
How to stop it from happening again
Before you sync, check your files for corruption. Use a tool like MP3val or just play each file in Windows Media Player to make sure it works. If a file skips or errors, delete it and get a fresh copy. Also, always safely eject your device before unplugging—pulling it out mid-sync corrupts the file system.
Real talk: 90% of the time, it's one bad file. Find that file, and the rest syncs fine. Don't waste time reinstalling Windows Media Player or messing with registry keys—that's overkill for this error.