Program: 7901
Project: 7901
Buggy source:
public void startThread(){
  enabled=true;
  runThread=new Thread(new Runnable(){
    public void run(){
      while (enabled) {
        try {
          Set<Entry<Player,Long>> set=timeStamp.entrySet();
synchronized (sync) {
            Iterator<Entry<Player,Long>> it=set.iterator();
            while (it.hasNext()) {
              Entry<Player,Long> next=it.next();
              if ((System.currentTimeMillis() - timedelay) > next.getValue()) {
                Player reciever=playerMap.remove(next.getKey());
                Player sender=recieverPlayerMap.remove(reciever);
                it.remove();
                if (sender != null && reciever != null && sender.isOnline() && reciever.isOnline()) {
                  ItemStack item=sender.getInventory().getItemInHand();
                  if (item.getTypeId() == itemId && item.getAmount() >= amountRequired) {
                    item.setAmount(item.getAmount() - amountRequired);
                    if (item.getAmount() <= 0) {
                      sender.getInventory().remove(item);
                    }
                    if (reciever.getHealth() + healamount > maxhealth)                     reciever.setHealth(maxhealth);
 else                     reciever.setHealth(healamount + reciever.getHealth());
                    if (reciever.equals(sender)) {
                      sender.sendMessage("String_Node_Str");
                    }
 else {
                      sender.sendMessage("String_Node_Str" + reciever.getName());
                      reciever.sendMessage(sender.getName() + "String_Node_Str");
                    }
                  }
 else {
                    sender.sendMessage("String_Node_Str");
                    if (!reciever.equals(sender))                     reciever.sendMessage(sender.getName() + "String_Node_Str");
                  }
                }
              }
            }
          }
          Thread.sleep(1000);
        }
 catch (        Exception ex) {
        }
      }
    }
  }
);
  runThread.start();
}

Fixed version (ground truth):
public void startThread(){
  enabled=true;
  runThread=new Thread(new Runnable(){
    public void run(){
      while (enabled) {
        try {
          Set<Entry<Player,Long>> set=timeStamp.entrySet();
synchronized (sync) {
            Iterator<Entry<Player,Long>> it=set.iterator();
            while (it.hasNext()) {
              Entry<Player,Long> next=it.next();
              if ((System.currentTimeMillis() - timedelay) > next.getValue()) {
                Player reciever=playerMap.remove(next.getKey());
                Player sender=recieverPlayerMap.remove(reciever);
                it.remove();
                if (sender != null && reciever != null && sender.isOnline() && reciever.isOnline()) {
                  ItemStack item=sender.getInventory().getItemInHand();
                  if (item.getTypeId() == itemId && item.getAmount() >= amountRequired) {
                    if (item.getAmount() == amountRequired) {
                      sender.getInventory().remove(item);
                    }
 else {
                      item.setAmount(item.getAmount() - amountRequired);
                    }
                    if (reciever.getHealth() + healamount > maxhealth)                     reciever.setHealth(maxhealth);
 else                     reciever.setHealth(healamount + reciever.getHealth());
                    if (reciever.equals(sender)) {
                      sender.sendMessage("String_Node_Str");
                    }
 else {
                      sender.sendMessage("String_Node_Str" + reciever.getName());
                      reciever.sendMessage(sender.getName() + "String_Node_Str");
                    }
                  }
 else {
                    sender.sendMessage("String_Node_Str");
                    if (!reciever.equals(sender))                     reciever.sendMessage(sender.getName() + "String_Node_Str");
                  }
                }
              }
            }
          }
          Thread.sleep(1000);
        }
 catch (        Exception ex) {
        }
      }
    }
  }
);
  runThread.start();
}