Hi. I contacted Apple iTunes support by email through this link:
http://www.apple.com/support/itunes/store/browser/. The category I chose was "connection," and the sub-category I chose was "I receive an error message..."
I commented that "I receive the following message when attempting to open my shopping cart: "We could not complete your iTunes Store request. An unknown error occurred (5002)."
They replied, "The error you are experiencing is probably due to one of the items in your cart, or the number of items in your cart...
...Should you continue to experience an issue with your shopping cart, please reply to this email with permission to clear your cart."
The entire process took a little over a day from my submitting the support email, to resolution of the issue.
A note about the wishlist. You cannot save albums, only songs by dragging directly from the iTunes Store.
Good Luck.