Encryption => 'EXP_CRYPT',
or
Encryption => "EXP_CRYPT",

##</code><code>##

  return _croak_or_return (undef, $die, $dbg_flg,
                           "Encryption mode unknown!  ($encrypt_mode)")
      if ( $encrypt_mode ne IMP_CRYPT && $encrypt_mode ne EXP_CRYPT &&
           $encrypt_mode ne CLR_CRYPT );


##</code><code>##

use constant EXP_CRYPT => "E";

##</code><code>##

Encryption => Net::FTPSSL::EXP_CRYPT,