Calculating Maximum Lots

I have written an indicator to calculate your lot size and maximum lot size based of percent of account you are risking and stoploss distance.

 It works most of the time on most pairs. But, every so often I get an insufficient funds error even though I am using the calculated lot size based on risk and SL which is less than my calculated maximum lot size. Could someone please look at my code and tell me what is wrong?

Kind Regards,

Tom 

//+------------------------------------------------------------------+
//|                                                    Lots_Size.mq4 |
//|                                     Copyright 2015, Tom Parimore |
//|                                              tparimore@yahoo.com |
//+------------------------------------------------------------------+
#property copyright "Tom Parimore"
#property link      "tparimore@yahoo.com"

// Last Updated  9/28/15  9:00 PM


   extern double Stop_Loss    = 10.0;  // pips
   extern double Percent_Risk =  3.3;
   extern bool   Show_Risk    =  true;
   extern string  xxxxxxxxxxxx  = "**************************************************************";
   extern int Corner = 1;
   extern int XDISTANCE1 = 25;
   extern int YDISTANCE  = 85;
   

#property indicator_chart_window
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  { 
    return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
    ObjectDelete("LotTitle");
    ObjectDelete("LotInput");
    ObjectDelete("LotMax");
    ObjectDelete("LotRisk");
    
    return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()
  {                
    double DPPPL = MarketInfo(Symbol(), MODE_TICKVALUE)*10;    // Dollars Per Pip Per Lots (DPPPL)
    
    
    string Text[4];                     // Declaring a string array
    color  Color[2];                    // Declaring an array of colors      
                     
    Color[0]= Yellow;                   // Object color ..
    Color[1]= Gray;


    ObjectCreate("LotTitle", OBJ_LABEL, 0, 0, 0);                // Creating obj.
    ObjectSet("LotTitle", OBJPROP_CORNER, Corner);               // Reference corner
    ObjectSet("LotTitle", OBJPROP_XDISTANCE, XDISTANCE1);        // X coordinate
    ObjectSet("LotTitle", OBJPROP_YDISTANCE, YDISTANCE);         // Y coordinate

    ObjectCreate("LotInput", OBJ_LABEL, 0, 0, 0);              // Creating obj.
    ObjectSet("LotInput", OBJPROP_CORNER, Corner);             // Reference corner
    ObjectSet("LotInput", OBJPROP_XDISTANCE, XDISTANCE1);      // X coordinate
    ObjectSet("LotInput", OBJPROP_YDISTANCE, YDISTANCE+20);    // Y coordinate
   
    ObjectCreate("LotMax", OBJ_LABEL, 0, 0, 0);                 // Creating obj.
    ObjectSet("LotMax", OBJPROP_CORNER, Corner);                // Reference corner
    ObjectSet("LotMax", OBJPROP_XDISTANCE, XDISTANCE1);         // X coordinate
    ObjectSet("LotMax", OBJPROP_YDISTANCE, YDISTANCE+40);       // Y coordinate
    
    ObjectCreate("LotRisk", OBJ_LABEL, 0, 0, 0);             // Creating obj.
    ObjectSet("LotRisk", OBJPROP_CORNER, Corner);            // Reference corner
    ObjectSet("LotRisk", OBJPROP_XDISTANCE, XDISTANCE1);     // X coordinate
    ObjectSet("LotRisk", OBJPROP_YDISTANCE, YDISTANCE+60);   // Y coordinate
                
    
    double AFM  = AccountFreeMargin();
    double MRPL = MarketInfo(Symbol(),MODE_MARGINREQUIRED);  // Margin Requirement Per $100k (1 Lot)
    
    double DRSK = AFM * Percent_Risk / 100;   // Dollar Risked
    if (MRPL==0)return(0);
    double MAXL = floor((AFM - DRSK)/MRPL*100)/100; // Max Lots with Dollar Risk
    double MAXDPP = MAXL * DPPPL;    // Dollar per pip with Max Lots
    if (MAXDPP==0)return(0);
    double MAXSL  = DRSK / MAXDPP;   // Stop Loss with Max Lots (Trade will margin out at MAXSL)
    if (DPPPL==0)return(0);
    double Lots = floor(DRSK / (DPPPL * Stop_Loss)*100)/100;
    double DPP  = Lots * DPPPL;
    
  
      
    
    Text[0]=  "Lots    SL    $/PIP";
    Text[1] = "Input:   " +  DoubleToStr(Lots,2) + "   " + DoubleToStr(Stop_Loss,1) + "   $" + DoubleToStr( DPP,2);
    Text[2] = "Max:    " +   DoubleToStr( MAXL,2) + "   " +  DoubleToStr( MAXSL,1)  + "   $"  + DoubleToStr( MAXDPP,2);
    if(Show_Risk) Text[3] = "Risk:    " +  DoubleToStr(Percent_Risk,1)  + "%       $" + DoubleToStr( DRSK,2);
    else Text[3] = ""; 

             
    ObjectSetText("LotTitle",     Text[0],10,"Arial",Color[0]);
    if(Lots <= MAXL ) ObjectSetText("LotInput",   Text[1],10,"Arial",Color[0]);
    else              ObjectSetText("LotInput",   Text[1],10,"Arial",Color[1]);
    ObjectSetText("LotMax",      Text[2],10,"Arial",Color[0]);
    ObjectSetText("LotRisk",  Text[3],10,"Arial",Color[0]);
    

    
   
   return(0);
  }
//+------------------------------------------------------------------+