This error occurred on iPhone 3GS New Bootrom when once you restored to custom firmware of Old bootrom. Once you get this error message you will never ever restore to any other firmwares even the current stock firmware. And your iPhone will be appeared with white screen and the iTunes is waiting for iPhone to be restored forever, many other error codes appeared in iTuens after trying some fix like trying to restore with DFU Mode, Recovery Mode and etc...
Definitely there is only way out of this misery, remove the battery off the iPhone Logic board for about one or two hours, After that assemble it back together.
After that restore your iPhone with the right firmware accordingly.
Congratulation your iPhone is back to live..!!