Multiple buffers in single advisor. CopyBuffer return error 4806

Question

In advisor used 3 Moving Average and each MA has its own buffer, but CopyBuffer never returns requested bars counter for a second MA. Only first MA ExtFastBuffer got buffer values, everything else stays empty and theirs CopyBuffer return error 4806. What is my mistake?

#property indicator_buffers 3

input ENUM_TIMEFRAMES ma_fast_timeframe = PERIOD_M1;
input int ma_fast_period = 2;
input ENUM_APPLIED_PRICE ma_fast_price_type = PRICE_MEDIAN;

input ENUM_TIMEFRAMES ma_middle_timeframe = PERIOD_M1;
input int ma_middle_period = 15;
input ENUM_APPLIED_PRICE ma_middle_price_type = PRICE_MEDIAN;

input ENUM_TIMEFRAMES ma_slow_timeframe = PERIOD_M1;
input int ma_slow_period = 30;
input ENUM_APPLIED_PRICE ma_slow_price_type = PRICE_MEDIAN;

int ExtFastHandle;
int ExtMiddleHandle;
int ExtSlowHandle;

double ExtFastBuffer[];
double ExtMiddleBuffer[];
double ExtSlowBuffer[];

//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
int OnInit()
  {
   SetIndexBuffer(0, ExtFastBuffer, INDICATOR_CALCULATIONS);
   SetIndexBuffer(1, ExtMiddleBuffer, INDICATOR_CALCULATIONS);
   SetIndexBuffer(2, ExtSlowBuffer, INDICATOR_CALCULATIONS);

   IndicatorSetInteger(INDICATOR_DIGITS,_Digits+1);

   ExtFastHandle = iMA(NULL, ma_fast_timeframe, ma_fast_period, 0, MODE_SMA, ma_fast_price_type);
   ExtMiddleHandle = iMA(NULL, ma_middle_timeframe, ma_middle_period, 0, MODE_SMA, ma_middle_price_type);
   ExtSlowHandle = iMA(NULL, ma_slow_timeframe, ma_slow_period, 0, MODE_SMA, ma_slow_price_type);

   if(ExtFastHandle == INVALID_HANDLE || ExtMiddleHandle == INVALID_HANDLE || ExtSlowHandle == INVALID_HANDLE)
     {
      Print("Error creating MA indicator-----------------------------------------------------------------------");
      return(INIT_FAILED);
     }

   return(INIT_SUCCEEDED);
  }


//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
void OnTick()
  {
   int startFromIndex = 0;
   int bufferSize = 2;

//---------------- Fast MA
   if(CopyBuffer(ExtFastHandle, 0, startFromIndex, bufferSize, ExtFastBuffer) < 2)
     {
      Print("Loading ExtFastHandle failed ", GetLastError());
     }
   ENUM_ORDER_TYPE fastDir = ExtFastBuffer[0] == ExtFastBuffer[1] ? NULL : (ExtFastBuffer[0] < ExtFastBuffer[1] ? ORDER_TYPE_BUY : ORDER_TYPE_SELL);

//---------------- Middle MA
   if(CopyBuffer(ExtMiddleHandle, 1, startFromIndex, bufferSize, ExtMiddleBuffer) < 2)
     {
      Print("Loading ExtMiddleHandle failed ", GetLastError());
     }
   ENUM_ORDER_TYPE middleDir = ExtMiddleBuffer[0] == ExtMiddleBuffer[1] ? NULL : (ExtMiddleBuffer[0] < ExtMiddleBuffer[1] ? ORDER_TYPE_BUY : ORDER_TYPE_SELL);

//---------------- Slow MA
   if(CopyBuffer(ExtSlowHandle, 2, startFromIndex, bufferSize, ExtSlowBuffer) < 2)
     {
      Print("Loading ExtSlowHandle failed ", GetLastError());
     }
   ENUM_ORDER_TYPE slowDir = ExtSlowBuffer[0] == ExtSlowBuffer[1] ? NULL : (ExtSlowBuffer[0] < ExtSlowBuffer[1] ? ORDER_TYPE_BUY : ORDER_TYPE_SELL);

   string fast = fastDir == NULL ? "EMPTY" : fastDir == ORDER_TYPE_BUY ? "BUY" : "SELL";
   string middle = middleDir == NULL ? "EMPTY" : middleDir == ORDER_TYPE_BUY ? "BUY" : "SELL";
   string slow = slowDir == NULL ? "EMPTY" : slowDir == ORDER_TYPE_BUY ? "BUY" : "SELL";
   Comment("Fast: ", fast, " Middle: ", middle, " Slow: ", slow);
  }
//+------------------------------------------------------------------+

Answer 1

Have a look at the sample EA's like EMA or MACD.

1. No need in SetIndexBuffer calls in the EA, they are used in indicators.

2. Second parameter in CopyBuffer is the number of the indicators' buffer. So if MA has only one buffer, use 0 all the time. If indicator has two buffers, like MACD, main line would have index 0, signal line would be called with index 1.

   //---------------- Middle MA
   if(CopyBuffer(ExtMiddleHandle, 0, startFromIndex, bufferSize, ExtMiddleBuffer) < 2)  
     {  
      Print("Loading ExtMiddleHandle failed ", GetLastError());
     }  
   ENUM_ORDER_TYPE middleDir = ExtMiddleBuffer[0] == ExtMiddleBuffer[1] ? NULL : (ExtMiddleBuffer[0] < ExtMiddleBuffer[1] ? ORDER_TYPE_BUY : ORDER_TYPE_SELL);
   
   //---------------- Slow MA  
   if(CopyBuffer(ExtSlowHandle, 0, startFromIndex, bufferSize, ExtSlowBuffer) < 2)  
     {  
      Print("Loading ExtSlowHandle failed ", GetLastError());
     }  
   ENUM_ORDER_TYPE slowDir = ExtSlowBuffer[0] == ExtSlowBuffer[1] ? NULL : (ExtSlowBuffer[0] < ExtSlowBuffer[1] ? ORDER_TYPE_BUY : ORDER_TYPE_SELL);