ener.hlp (Topic list)
Variable required (ERR: 40)
■ At compile time, Visual Basic encountered an INPUT, LET,
  READ, or SHARED statement without a variable argument.
 
■ At run time, a GET or PUT statement did not specify a
  variable when an operation was performed on a file opened
  in binary mode.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.