dunit2

I am trying to recover data from an external USB drive from windows XP (I know, I know, but I refused to go to Windows Vista, or 8 and just couldn't pull the trigger on 7). I am using the free version of Recuva and everything ssems to show up fine. When I use the restore on a file, the window comes up with the status bar moving across is for a bit like it is doing it's recovery, but then I get the message, "the device is not ready". Anyone no what this means?