I have an IPOD Nano 4th Generation 8GB and need to restore to factory settings as want to sell it; however it will not reset and when plugged into my MAC it says firmware corrupt? CAn anyone shed light on what i can do to overcome this issue?

I have an IPOD Nano 4th Generation 8GB and am unable to restore it back to factory settings even when it is connected to my MAC. I have tried the menu/select hold but is not doing anything. When connected to the MAC and select restore in itunes it comes up with 'Firmware Corrupt'. It also states the IPOD is up to date. I have the latest operating system on my MAC and wonder if this may be part of the issue?

Can anyone shed light as to what i can do to reset it back to factory settings as would like to sell it and ensure it is ready for the new owner.

Thanks

jay68g