Thank you kado897 for taking the time to try and help

I have however seen the Microsoft answer (on several forums) and studied it - none of the scenarios seem to fit the specific error I'm getting, wish they did! I did try the scenario 3 answer but that didn't apply either.
I don't see how "saved games" would affect a backup - it seems so trivial but of course it isn't if it prevents a successful backup. There is quite a lot of information backed up on the usb drives I used, is it useless - after all the backup did complete, just skipped this strange file. (Just in case it was anything to do with games statistics on the standard games installed on most computers I cleared them as the
second backup was starting, same end result - this error)
Would you explain in more detail what you mean by 'run the backup configuration again' - on one occasion when I opted to choose what to back up I was totally confused as to what to select, so I went back and opted for the "let Windows choose" option as it seemed straightforward, maybe it isn't?
I'll be grateful for any help you or anyone else can offer - I am not particularly technical so I need all the help I can get.