it works fine for me

instead of this line

if ($calc( $regex( $2 ,rock) + $regex( $2 ,paper) + $regex( $2 ,scissors) ) != 1) { msg $chan [4 $+ $nick $+ ] You've got to choose Rock, Paper or Scissors! | halt }

you can use

if (!$regex($2,/^(rock|paper|scissors)$/i)) { msg $chan [4 $+ $nick $+ ] You've got to choose Rock, Paper or Scissors! | halt }

or

if (!$istok(rock paper scissors,$2,32)) { msg $chan [4 $+ $nick $+ ] You've got to choose Rock, Paper or Scissors! | halt }

they both work just fine.