iTunes error -4 and iPhone OS 3.0
2009 June 17
Trying to update to the new iPhone OS v3.0 and was repeatedly getting this error message in iTunes.
We could not complete your iTunes Store request.
An unknown error occured (-4).
There was an error in the iTunes Store. Please try again later.
Apparently, Rich Hauck has the solution.
1. Quit iTunes
2. Navigate to System/Library/Extensions and delete AppleMobileDevice.kext (you may be prompted to enter your admin information)
3. Restart iTunes
Directions are also official via Apple Support.