iPhone won't restore after backup

I have just tried to instal 6.1.1 via iTunes.

The iTunes aparently backed up my iPhone 4S, as the backup shows in iTunes (Preferences-Devices). Now iTunes states I need to restore my iPhone to continue, but after a few minutes of trying to restore I get the message 'unknown error occured' . Thing is it does seem to recognise my iPhone with the name I've given it??

In short - help!