[Muuss]

sub EVENT_ITEM {
  if ($class == Warrior)
    (plugin::check_handin(\%itemcount, 6164 => 1)) {
      quest::summonitem(62189);
      quest::exp(750);
      quest::emote("smiles warmly as he hands you your weapon.");
      quest::ding(); 
    }

missing && between $class=="Warrior" and the check_handin
or miswritten tests.

I would write it that way :

sub EVENT_ITEM {
  if (($class == "Warrior") && (plugin::check_handin(\%itemcount, 6164 => 1))) {
      quest::summonitem(62189);
      quest::exp(750);
      quest::emote("smiles warmly as he hands you your weapon.");
      quest::ding(); 
    }

  if (($class == "Paladin") && (plugin::check_handin(\%itemcount, 6164 => 1))) {
      quest::summonitem(62189);
      quest::exp(750);
      quest::emote("smiles warmly as he hands you your weapon.");
      quest::ding(); 
    }

   ...
   ...
  plugin::return_items(\%itemcount);
}