Q: An unknown error occurred (4002).

Store > Turn off iTunes Match

Store > Update Genius (let it run + finish)

Store > Turn on iTunes Match (set it going and it should work properly)

This solved my Error 4002 issue.  Thank you!

I couldn't download any updated Apps from iTunes -- this procedure worked for that too. Thanks

So, why is Genius connected to iTunes match?

And now I get the same error while Genius is updating.

This was it, thanks, gonna share it in the other questions referring to this.

I was getting the same error when updating Genius. From the Store menu, turn Genius off then back on then update. This cleared the error for Genius for me. Then turn iTunes Match back on and you should be all set.

Solved this very frustrating problem! Thanks!!

That fixed it for me too.. Mine would give me that error if Genius data was updating in iTunes. I turned Genius OFF then back ON using the Store Menu commands and the problem went away

This stream was the best about this problem.  The key is that if you use ITunes Match, you have to turn it off before you can turn off Genius.  All other posts tell you to turn Genius off and on, but you don't have the option unless you first turn off ITunes Match.  Thanks for the info.

Hi, Keely

Your note really helped me.  But when I tried to update Genius I got the error 4002 error message again.  So maybe the best procedure (for people who have this additional problem) is to add a step.  This worked for me!

Store > Turn off iTunes Match

Store > Turn off Genius

Store > Update Genius (let it run + finish)

Store > Turn on iTunes Match (set it going and it should work properly)

It does work for me!!! Thanks!!!!

Thank you soooo much it fixed

I am having this issue on a PC running Windows7. Just updated my version to the latest release 11/2014 (what ever number release that would be). I keep getting Error 4002 when I try to update Genius Results. I DO NOT use iTunes Match. When I turned Genius OFF in the Store, it began to delete all of my Genius Results. Anyone?

This problem has been annoying me for a long time, and today I finally decided to find a solution.  Your suggestion worked like a charm.  Thank you!