1. Activate DFU Mode
2. Download Firmware Files
3. Make sure you have SHSH Blobs Saved on Cydia
4. Check for Updates
5. Repair Registry Errors
Activate DFU Mode
Do not get confused between DFU Mode and Recovery Mode. Both are different terms. Put your iPhone device into the DFU Mode to fix error 1015.
1. Connect the iPhone to your computer.
2. Turn your iPhone off.
3. Double click iTunes desktop shortcut.
4. Hold the Power & Home buttons simultaneously. Keep holding them for approximately 12-15 seconds.
5. Release the Power button but keep holding the Home button.
6. Once your computer recognizes the newly connected USB connection, please do release the Home button.
7. iTunes shall recognize your iPhone automatically. Wait few seconds.
Download Firmware Files
You might need to download the required iOS 4.0.1 IPSW Firmware. Click here to download the firmware and fix error 1015.
Make sure you have SHSH Blobs Saved on Cydia
In order to prevent error 1015 make sure you have the SHSH Blobs saved on Cydia. The firmware version you’re downgrading/ restoring should have SHSH Blobs files saved. Without it the downgrade or restore process fails.
Check for Updates
Check for application updates and download-install them. You might have an older version of iTunes installed. Latest version includes patches & updates that resolve application bugs and errors.
In addition to this download and install Windows updates. Get latest patches from the Microsoft website as shown here:
1. Click Start | All Programs | Windows Update.
2. Click Check for Updates button.
3. The update check-up process may start. Please wait while.
4. Click Download and Install Updates button.
Repair Registry Errors
Scan and repair problems detected in your Registry. Use a Registry Cleaner software to do so.
1. Download Registry Cleaner software-> RegInOut
2. Install and run it.
3. Start full scan.
4. Fix all errors detected.