|perfib_perfdata files are being used by Windows so they cannot be copied.|
They are performance data files.
There is no need to back them up anyway as they are re-created every time you start Windows, so it's pointless backing them up even if you could.
They are usually located inside your Local Settings/Temp folder which does not need to be backed up either, it's pointless backing up temporary files. Exclude the Temp folder when you are backing up your data and you won't get that error.