A lot of people have been getting this error - iTunes Error 5002. When I got this error, I promptly sat down to find out more about this and how to get rid of it. During the course of my research, in which I involved internet, forums, Apple help desk etc, this is what I learnt and which I am sharing with you all to make it easy for everybody to resolve this error.
First of all, make sure you get the error with iPod touch while trying to upgrade apps in iTunes version 8.
The best approach to handle this error is to do the following.
