“An unknown error occurred (9006).”i Tunes error 9006 could crop up due to more than one reasons such as lack of proper internet connection, faulty USB port etc.
You can easily overpower this issue with a few tricks.
The App you've tried to download in i Tunes couldn't be saved. Use Tiny Umbrella or redsn0w to kick it out of Recovery Mode.
This error is common when downgrading i Phones and 3G i Pads.
Error occurs when one uses the "last ditch" method for preventing baseband updates on the i Phone 4.
Use Tiny Umbrella and "Kick Device Out Of Recovery" to boot.
Missing system files or corrupt data in i Tunes installation.
Try to uninstall i Tunes, restart computer, install again. i Tunes expected the device to be in a different state (Example: booted into i OS rather than jumping to i BEC).