Existing users, 
iTunes 8: Workaround for 5002 Unknown Error When Trying to Update Apps
Posted 10 September 2008 @ 9am in Troubleshooting
Users and one iPhone Atlas staffer are reporting problems with the iPod touch while upgrading apps in iTunes 8. See this Apple discussion.
We’ve discovered this workaround: update the apps from the iPod Touch itself and then sync your iPod Touch with iTunes 8. ITunes 8 transfers the purchases to the iTunes library on your computer and the updates are then available for other devices you might have like an iPhone or other iPods. The error no longer appears.
Since there have been reported problems with on device updates in the past it’s recommended that you closely monitor the device. Keep it from falling asleep and/or running out of power by plugging it into your computer or an AC adapter during the update installations.
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3 Comments
Posted by King Antoine XIII
10 September 2008 @ 8pm
FIX | Error 5002:
Delete any apps in iTunes that have a generic icon, then click the Check for Updates link again. Ta-da!
You can then redownload the deleted app(s).
Posted by king avery
11 September 2008 @ 11pm
Upgrade to iTunes 8, then:
1 Drag the Mobile Applications folder from ~/Music/iTunes to the desktop
2 Open iTunes WITHOUT THE IPHONE/IPOD CONNECTED and select all your applications and delete them. (if your iPhone/iPod were connected, it would now start helpfully deleting apps)
3. When they’re all gone, quit iTunes
4. Start iTunes again and verify that you have no apps listed.
5. Drag your the Mobile Applications folder from the Desktop to your open iTunes window — if you have default iTunes settings (copy/manage my music), then iTunes will start re-adding your applications.
6. Read the iTunes notices carefully — you will likely get something like “an OLDER version of this app already exists, do you want to replace it” (you DO), or “a NEWER version of this app already exists, do you want to replace it” (you DON’T), or sometimes a mention that this app already exists as the same version (replace it).
7. Quit iTunes, then restart it to “set” the changes
–
This also fixes the 5002 errors as well.
Posted by barnesjon
12 September 2008 @ 11pm
I think itunes is terrible, here is a blog post about why itunes will eventually die. http://tinyurl.com/45d9yy