Array out of range in a custom average function

Question

So im writing a custom atr indicator with multipliers (Display 2 lines, first line is raw atr value, and second one is atr*1.5), but for some reason it says "array out of range (66,28)", where I calculate my average of the true range. I did use SetIndexBuffer on my arrays, so the problem should be in OnCalculate().

This is what I have in my OnCalculate function:

for(int i=0;i<rates_total-prev_calculated;i++){
      TRBuffer[i] = MathMax(MathMax(high[i]-low[i], MathAbs(high[i]-close[i+1])),MathAbs(low[i]-close[i+1]));
      if(prev_calculated-1<=ATRLength){
         double sumTR=0;
         for(int j=0;j<ATRLength;j++){
            sumTR+=TRBuffer[i+j];
         }
         double atr = sumTR/ATRLength;
         TRBuffer[i] = atr*TPMultiplier;
         SLBuffer[i] = atr*SLMultiplier;
      }
   }

Answer 1

Found the answer, this is the final code.

if(rates_total<=ATRLength)
      return 0;
   int limit = rates_total-prev_calculated;
   if(prev_calculated>0)
      limit++;
   double ATRVal;
   for(int i=limit-2; i>1; i--){
      TRBuffer[i] = MathMax(MathMax(high[i]-low[i], MathAbs(high[i]-close[i+1])),MathAbs(low[i]-close[i+1]));
      ATRVal = iMAOnArray(TRBuffer, 0, ATRLength, 0, MODE_SMA, i); 
      TPBuffer[i] = ATRVal*TPMultiplier;
      SLBuffer[i] = ATRVal*SLMultiplier;
   }