Why do I get OrderSend error on UK100?

Why in the following code do I get OrderSend error 131 on UK100 but not on EURUSD?

// Input variables                                    
input int MagicNumber = 101;                        
input int Slippage = 10;

input double LotSize = 0.1;  
input int StopLoss = 20;
input int TakeProfit = 20;

input int MaPeriod = 200;
input ENUM_MA_METHOD MaMethod = MODE_SMA;   
input ENUM_APPLIED_PRICE MaPrice = PRICE_CLOSE;

// Global variables
int gBuyTicket, gSellTicket;

// OnTick() event handler                
void OnTick()   // void doesnt use a return value
{
   // Current order counts     
   int buyCount = 0, sellCount = 0;  // sets object back to 0
   
   for(int order = 0; order <= OrdersTotal() - 1; order++) 
   {
      bool select = OrderSelect(order,SELECT_BY_POS);
      
      if(OrderMagicNumber() == MagicNumber && select == true) // recognises the magicnumber of order recognises magic number of EA realises theres been an order selected by OrderSelect () function
      {
         if(OrderType() == OP_BUY) buyCount++;
         else if(OrderType() == OP_SELL) sellCount++;
      }   
   }

   // Moving Average and Close price from last bar                Section 3
   double close = Close[1];                                           
   double ma = iMA(_Symbol,_Period,MaPeriod,0,MaMethod,MaPrice,1);    
           
   // Buy order condition                                     Section 4
   if(close > ma && buyCount == 0 && gBuyTicket == 0)
   {
      // Close sell order         OrderTotal() is a function that returns the amount of open orders.
      for(int order = 0; order <= OrdersTotal() - 1; order++)    // for loop finds any open orders
      {                         // 1      index in order pool
         bool select = OrderSelect(order,SELECT_BY_POS);   // selects the open order (Order index or order ticket depending on the second parameter.)(SELECT_BY_POS - index in the order pool) 
         
         if(OrderType() == OP_SELL && OrderMagicNumber() == MagicNumber && select == true) // checking its a sell checking magicnumber matches and it has selected an order
         {
            // Close order
            bool closed = OrderClose(OrderTicket(),OrderLots(),Ask,Slippage,clrRed);  // Notice you can input functions written OrderTicket() as parameters
            if(closed == true) order--;  // order -- decrements order from 1 to 0 so it will stop iterating
         }
      }
       
      // Open buy order                                                                                      Section 5
      gBuyTicket = OrderSend(_Symbol,OP_BUY,LotSize,Ask,Slippage,0,0,"Buy order",MagicNumber,0,clrGreen);
      gSellTicket = 0;

      // Add stop loss & take profit to Buy order
      if(gBuyTicket > 0 && (StopLoss > 0 || TakeProfit > 0))
      {
         bool select = OrderSelect(gBuyTicket,SELECT_BY_TICKET);
         
         // Calculate stop loss & take profit
         double stopLoss = 0, takeProfit = 0;
         if(StopLoss > 0) stopLoss = OrderOpenPrice() - (StopLoss * _Point);
         if(TakeProfit > 0) takeProfit = OrderOpenPrice() + (TakeProfit * _Point);
         
         // Verify stop loss & take profit
         double stopLevel = MarketInfo(_Symbol,MODE_STOPLEVEL) * _Point;
         
         RefreshRates();
         double upperStopLevel = Ask + stopLevel;
         double lowerStopLevel = Bid - stopLevel;
         
         if(takeProfit <= upperStopLevel && takeProfit != 0) takeProfit = upperStopLevel + _Point;
         if(stopLoss >= lowerStopLevel && stopLoss  != 0) stopLoss = lowerStopLevel - _Point; 
         
         // Modify order
         bool modify = OrderModify(gBuyTicket,0,stopLoss,takeProfit,0);
      }
   }
   
   
   // Sell order condition
   if(close < ma && sellCount == 0 && gSellTicket == 0)
   {
      // Close buy order
      for(int order = 0; order <= OrdersTotal() - 1; order++)
      {
         bool select = OrderSelect(order,SELECT_BY_POS);
         
         if(OrderType() == OP_BUY && OrderMagicNumber() == MagicNumber && select == true)
         {
            // Close order
            bool closed = OrderClose(OrderTicket(),OrderLots(),Bid,Slippage,clrRed);
            
            if(closed == true)
            {
               gBuyTicket = 0;
               order--;
            }
         }
      }
      
      // Open sell order
      gSellTicket = OrderSend(_Symbol,OP_SELL,LotSize,Bid,Slippage,0,0,"Sell order",MagicNumber,0,clrRed);
      gBuyTicket = 0;
      
      // Add stop loss & take profit to Sell order
      if(gSellTicket > 0 && (StopLoss > 0 || TakeProfit > 0))
      {
         bool select = OrderSelect(gSellTicket,SELECT_BY_TICKET);
         
         // Calculate stop loss & take profit
         double stopLoss = 0, takeProfit = 0;
         if(StopLoss > 0) stopLoss = OrderOpenPrice() + (StopLoss * _Point);
         if(TakeProfit > 0) takeProfit = OrderOpenPrice() - (TakeProfit * _Point);
         
         // Verify stop loss & take profit
         double stopLevel = MarketInfo(_Symbol,MODE_STOPLEVEL) * _Point;
         
         RefreshRates();
         double upperStopLevel = Ask + stopLevel;
         double lowerStopLevel = Bid - stopLevel;
         
         if(takeProfit >= lowerStopLevel && takeProfit != 0) takeProfit = lowerStopLevel - _Point;
         if(stopLoss <= upperStopLevel && stopLoss != 0) stopLoss = upperStopLevel + _Point; 
         
         // Modify order
         bool modify = OrderModify(gSellTicket,0,stopLoss,takeProfit,0);
      }
   }
}