I'm not familiar with Lapper, but wouldn't this be enough:
$ListP = getListOfPlayers();
$playerCount = count($ListP);
WHILE($ListP[$player] != "" )
$player1 = $ListP[$player];
$player=$player+1;
$rr = round(ToNum(RandomNum(1,$playerCount)),0)."";
SetPlayerVar($ListP[ToNum($rr)],"CurrentJob", 4);
privmsg("^1".$player);
ENDWHILE

If this doesn't work, then I'd assume you would need second loop.

You forgot break; at the end of case.
Simpler example of this error: https://stackoverflow.com/a/6696709