hello there,i updated my iphone 3G 4.1 to 4.2.1 but i can not recover it because of the error 1015 that appears after failure of restoring firmware. Please help me solve this problem,this phone has very important documents in it. thank you for help.

error 1015 usually suggests that the phone has been jailbroken. Has it?

Is the iPhone jailbroken or was jailbroken?. In the article " http://support.apple.com/kb/TS3694 " it says:

Errors related to downgrading iOS

The required resource can't be found: This alert message occurs when your device has a newer version of iOS than what is available in iTunes. When troubleshooting a device that presents this alert message, go toSettings > General > About and check the version of iOS on the device. If it's newer than the latest released iOS version, the device may have a prerelease developer version of iOS installed. Installing an older version of iOS over a newer version isn't supported.

Error 1015: This error is typically caused by attempts to downgrade the software for an iPhone, iPad, or iPod touch. This can occur when you attempt to restore using an older .ipsw file. Downgrading to a previous version isn't supported. To resolve this issue, attempt to restore with the latest iPhone, iPad, or iPod touch software available from Apple. This error can also occur when an unauthorized modification of the iOS has occurred and you're now trying to restore to an authorized, default state.