iTunes 5103 Error

Here’s the solution on Apple’s support site.

1. Quit iTunes and any other open applications until only Finder is open.
2. Choose Go > Go to Folder.
3. Type /Users/Shared/SC Info and click Go.
4. If Finder is not already set to column view, set it by choosing View > as Columns.
5. Select the SC Info folder and move it to the Trash by choosing File > Move to Trash.
6. Open iTunes.

I removed the bit that said to restart your computer, because I didn’t, and it still worked.