Why do I keep getting an "error 5002" when trying to purchase my wish list?

http://support.apple.com/kb/TS3297

Maybe this might help.

I've been trying to figure this out for the past four days myself. I tried everything I could to reset my account information since most of the forums indicated the problem was with my payment information. That didn't ring true for me because I regularly make purchases with no problem. In my case, the problem was that one of the songs I was trying to purchase had been purchased previously. I found this out when I went to each song in my wish list individually and hit the buy button. Surprisingly, each song was purchased and downloaded successfully. When I got to the sixth song or so in my wishlist, iTunes told me that I had already purchased that song and asked if I wanted to download it again. I said yes. I then hit the buy all button for the remaining songs (the behavior that had not worked previously and generated the 5002 error) and the download happened properly.

I realize that the 5002 error seems to be generated by multiple issues, but that is what worked for me. Perhaps you could try the same approach and see what happens if you haven't already resolved your issue. Good luck.

The same thing happened to me. As HolidayPhotography said my issue was a song that I had added to my wish list, then eventually purchased it but it was still in my wishlist. I removed it and it worked fine.