Error 1015: This error is caused by attempts to downgrade the iPhone, iPad, or iPod touch's software. This can occur when you attempt to restore using an older .ipsw file. Downgrading to a previous version is not supported. To resolve this issue, attempt to restore with the latest iPhone, iPad, or iPod touch software available from Apple.
Säker på att det går att downgrade'a från 4.0?
Annars testa något sånt här typ:
# The restore might get stuck and you’ll get an error 1015 message.
# Ignore it and reboot your iPhone using the power + home buttons.
# You’ll now see the USB and iTunes logo in the iPhone display. This means that firmware 3.1.2 is installed. But right now, the phone is stuck in a DFU loop.
# To fix this, you’ll need to use iRecovery. Follow this guide (http://www.ihackintosh.com/2009/07/irecovery-iphone-recovery-mode-loop-restart/) at iHackintosh for it.