Disk Utility: How to Restore Failure Could Not Validate Source?

I had backed up an older G4 with a disk image of the boot disk. I had severe problems, so I reformatted the boot drive and started a restore (using disk utility from the startup disk). The restore started fine and ran for a while but then 'stalled.' The 'progress' bar stopped, and the system kept hitting the Utility DVD install disk non-stop (as shown by the disk access light). When I try again, I immediately get a 'Restore Failure - Could not validate source - error 254.'

"Restore Failure Could Not Validate Source" is a common error users encounter when restoring a disk image (.dmg or .iso) to a USB drive or external hard drive using Disk Utility in macOS.  If you lose data or DMG files during the process, remember to use data recovery software - EaseUS Data Recovery Wizard for Mac to recover them.

Here's how you can fix this issue:

• Open Terminal on your Mac (you can find it under Utilities or by searching for it using Spotlight).

• Convert the .iso file to .img using the 'hdiutil' command. For example: hdiutil convert -format UDRW -o /path/to/target.img /path/to/source.iso
• Replace '/path/to/target.img' with the path where you want to store the converted file.
• This command will create a .img file with a .dmg extension (like target.img.dmg).
• You need to remove the .dmg extension. You can do this with the following command: mv /path/to/target.img.dmg /path/to/target.img
• Find the device identifier for your USB drive. You can use the following command: diskutil list

You should see a list of all your drives. Your USB drive should be something like /dev/disk2, /dev/disk3, etc.

• Unmount the USB drive using the following command (replace 'X' with your disk number): diskutil unmountDisk /dev/diskX
• Now, copy the .img file to your USB drive using the following command (again, replace 'X' with your disk number): sudo dd if=/path/to/target.img of=/dev/rdiskX bs=1m

Once the process is complete, your USB drive should be ready to use.