ener.hlp (Topic list)
Important Notice
The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.
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.