When you are trying to update or restore your iPhone or iPod touch with iTunes, the update or restore process may stop, and you may see an alert message in iTunes. You may also see the "Connect to iTunes" screen on your iPhone or iPod touch:
The alert message in iTunes may also include one of the following numbers (but is not limited to): 2, 4, 5, 6, 9, 13, 14, -18, 19, 20, 21, 23, 28, -48, -50, 1002, 1011, 1013, 1015, 1601, 1602, 1603, 1604, 1608, 1609, 1611, 1612, 1639, 2009, 3004, 3013, 3014, 3015, 9807, -9808, 9844.