Either the file you're trying to create is already open or you don't have rights to write to that location.  
  • If the file is already open, close the file before trying to export.  
  • If the file is not open but you are still getting the error message, it is possible your system doesn't allow you to save to that location.   This may be the case if you have recently updated Windows.   Newer Windows versions may have the c drive locked.   Your IT can give you access or save to a different location.