HOW TO fix “iphone could not be restored because the firmware is not compatible” error

“iPhone could not be restored because the firmware is not compatible"

People who have tried to downgrade their iPhone firmware from 4.0 to 3.1.2, tried to unlock it, or simply restore it to factory settings have run into this error. Here is what I tried that worked when I got this error when downgrading from iOS 4.0 to iOS 3.1.2 on my iPhone 3g :-

Just download an unmodified copy of the firmware from Apple’s website and then try to do a restore with that. It seems a copy of the firmware that has already been used for an earlier restore is somehow modified and causes this error when trying to restore again. This worked for me with iTunes 9.0. 

 Here are the direct links for iOS firmware for download from Apple’s website:-

iOS 3.1.2 direct links (iOS apple.com links):-

iPhone 2G: iPhone1, 1_3.1.2   _7D11_Restore.ipsw
iPhone 3G: iPhone1, 2_3.1.2_7D11_Restore.ipsw
iPhone 3GS: iPhone2, 1_3.1.2_7D11_Restore.ipsw

iPod Touch 1G: iPod1, 1_3.1.2_7D11_Restore.ipsw
iPod Touch 2G: iPod2, 1_3.1.2_7D11_Restore.ipsw
iPod Touch 3G: iPod3, 1_3.1.2_7D11_Restore.ipsw

iOS 3.1.3 direct links (iOS apple.com links):-

iPhone 2G: iPhone1,1_3.1.3_7E18_Restore.ipsw
iPhone 3G: iPhone1,2_3.1.3_7E18_Restore.ipsw
iPhone 3GS: iPhone2,1_3.1.3_7E18_Restore.ipsw

iPod touch 1G: iPod1,1_3.1.3_7E18_Restore.ipsw
iPod touch 2G: iPod2,1_3.1.3_7E18_Restore.ipsw

 iPod touch 3G: iPod3,1_3.1.3_7E18_Restore.ipsw