Here's an error that iTunes was throwing at me when I tried to update the applications on my iPhone:

We could not complete your iTunes Store request.
An unknown error occurred (5002).

There was an error in the iTunes store. Please try again later.

But every time I tried later I would get the same error. And as the days went by, the number of applications needing to be updated just kept going up.

Here's the fix.

Go to the applications screen in iTunes. You'll see one (maybe more) applications with an icon that looks like so:



To get rid of this 5002 error, you need to delete the applications that have this icon. Once you delete all of them, the updates will work. You can then go to the app store in iTunes and "rebuy" the applications that you had to delete. Since you already paid for them you will not be charged again.

It's a pain to go through this process, but if you are getting this error, this solution does work. If anyone has an easier way to solve this problem I'd love to hear it.