Delete Order

Hi,

Why if i run the script it doesn't work?

it says : Error 4109. Is something with with the code?

/+------------------------------------------------------------------+
//|                                               delete_pending.mq4 |
//|                                                                  |
//|                                                                  |
//+------------------------------------------------------------------+
#property copyright "Copyright © 2004, MetaQuotes Software Corp."
#property link      ""
#property show_confirm

double Slip;
bool result;
int start()
  {
  
//----

//----
   
   for (int f = 0; f < OrdersTotal(); f++)
      {
         OrderSelect(f,SELECT_BY_POS, MODE_TRADES);
         switch (OrderType())
            {
               case OP_BUY : result = OrderClose(OrderTicket(), OrderLots(), Bid, 3);
               case OP_SELL : result = OrderClose(OrderTicket(), OrderLots(), Ask, 3);
                        
               case OP_BUYLIMIT  : result = OrderDelete(OrderTicket());
               case OP_BUYSTOP   : result = OrderDelete(OrderTicket());
               case OP_SELLLIMIT : result = OrderDelete(OrderTicket());
               case OP_SELLSTOP  : result = OrderDelete(OrderTicket());
                        
            }
      }

   if(result == false)
      {
         Alert("Order " , OrderTicket() , " failed to close. Error:" , GetLastError() );
         Sleep(3000);
      }  
//----
   return(0);
  }
//+------------------------------------------------------------------+