OrderModify() - need some help please

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I am trying to modify an order that is current/open.  To keep the changes that I want to make very simple at this stage (I am just trying to get the code right) all that i am attempting to do is find the order and then change the arrow colour to blue, but I get an OrderModify error code 4109.

 

Anyone spot where I am making the error in the code? 

  
 int    i,Pos,Error;
   int    Total=OrdersTotal();
   
   if(Total>0)
   {for(i=Total-1; i>=0; i--) 
     {if(OrderSelect(i, SELECT_BY_POS, MODE_TRADES) == TRUE && OrderMagicNumber()==39379)
       { 
       bool res=OrderModify(OrderTicket(),OrderOpenPrice(),OrderStopLoss(),OrderTakeProfit(),0,Blue);}
            if(!res)
               Print("Error in OrderModify. Error code=",GetLastError());
            else
               Print("Order modified successfully.");
 

Error 4109 = "Trade is not allowed in expert properties"

You need to enable checkbox "Allow live trading" in the expert properties. 

 
Yes, but Live trading is active.  But perhaps this means the trade does not work on a practice account...  Does the code look OK to you?
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