I posted an old iPhone 4 to my sister (I'm in Australia; she's in Thailand) which was working fine both before and after she received it.
Recently it has started cutting off while being used - especially when using data - and saying there's 'no reception'. This was happening every couple of weeks.
My sister has been restoring the iPhone through iTunes each time this happens, which had been resolving the problem until it came back again.
Unfortunately now though it is no longer restoring through iTunes, and showing this error message:
The iPhone "iPhone" could not be restored. An unknown error occured (-1)
Obviously this is a pretty unhelpful error message. This Apple support page covers the next steps for most error types, but it appears that the error number
-1 is an error in and of itself!
The phone is now stuck on the usual restore screen:
What steps could we try to resolve this? Or is it likely that the phone is just too old and is suffering from software designed for newer iPhones? In case it is relevant, the phone has never been jailbroken and I (and my wife) have always been the original owners. It is a 4, not a 4S.