How to Fix Disappearing iPhone iPod Library Bug in iOS 4.2

Some iPhone, iPad, and iPod touch users who updated to the recently released iOS 4.2 have been experiencing issues with their iPod music library disappearing after the update is complete.

If when opening your iPod.app you find your library has disappeared, to do not fret. It hasn’t been deleted, it simply isn’t being seen by the iPod app due to a bug in iOS 4.2. The good news is there appears to be a simple fix:
1.Connect your iOS device to your Mac or PC and open iTunes
2. Select your device from the left column
3. Underneath your device in the left column, select ‘music” and play a song
4. Hit ‘Sync’ in iTunes to re-sync your music library
5. Open iPod.app on your iOS device and wait a moment while your library is repopulated.