You have an odd number of parameters. Add another ,_ after your last $chr(63).

So it would be:

Code:
alias replaceIt {
  return $replace($1-,$chr(96),_,$chr(126),_,$chr(33),_,$chr(64),_,$chr(35),_,$chr(36),_,$chr(37),_,$chr(94),_,$chr(38),_,$chr(42),_,$chr(40),_,$chr(41),_,$chr(45),_,$chr(43),_,$chr(61),_,$chr(123),_,$chr(125),_,$chr(91),_,$chr(93),_,$chr(92),_,$chr(124),_,$chr(59),_,$chr(58),_,$chr(39),_,$chr(34),_,$chr(44),_,$chr(46),_,$chr(60),_,$chr(62),_,$chr(47),_,$chr(63),_)
}