what is iTunes error 8003

Try deleting the partial cached downloads in the iTunes media folder.

That error is outlined in this Apple article -> iTunes: Advanced iTunes Store troubleshooting

"Error -50," "-5000," "8003," "8008," or "-42023"

These alerts occur due to timeouts or conflicts trying to write a file during download.

If you encounter this issue while accessing iTunes Store:

See iTunes 9: "One Moment Please" or "Error (-50)" message when accessing iTunes Store

If you encounter this issue while while downloading something from the iTunes Store:

Delete your iTunes Downloads folder, located in:

Mac OS X:
 ~/Music/iTunes/iTunes Media/Downloads Note: "iTunes Media" may appear as "iTunes Music. Also, the tilde (~) refers to your Home directory.

Windows Vista:
 \Users\username\Music\iTunes\iTunes Media\Downloads\

Windows 7:
 \Users\username\My Music\iTunes\iTunes Media\Downloads\

Windows XP:
 \Documents and Settings\username\My Documents\My Music\iTunes\iTunes Media\Downloads\

After locating your iTunes Downloads folder:

1. Quit iTunes.
2. Delete the Downloads folder on your computer.
3. Open iTunes.
4. Choose Store > Check for Available Downloads.
5. Enter your account name and password.