MT5 error 4802: Indicator cannot be created

What MQL5 says

4802 ERR_INDICATOR_CANNOT_CREATE

Indicator cannot be created

From MQL5's table of runtime errors, read 24 October 2026. An Expert Advisor reads it with GetLastError() after a call fails; the Experts tab prints what the EA logs.

What causes it

iCustom() couldn't find the indicator's .ex5. MQL5's iCustom page: it looks next to the calling program, then under MQL5\Indicators, and returns INVALID_HANDLE with 4802 when the file is in neither; an indicator that was never compiled has no .ex5 at all.

The fix in MQL5

Compile the indicator so its .ex5 exists, pass its name relative to MQL5\Indicators (a subfolder with a double backslash, "MyFolder\\MyIndicator"), and check the handle against INVALID_HANDLE.

int h = INVALID_HANDLE;

int OnInit()
  {
   h = iCustom(_Symbol, PERIOD_CURRENT, "MyIndicator.mq5");   // the source file, not the .ex5 MT5 loads
   return(INIT_SUCCEEDED);
  }

int h = INVALID_HANDLE;

int OnInit()
  {
   // the compiled indicator, relative to MQL5\Indicators, double backslash for a subfolder
   h = iCustom(_Symbol, PERIOD_CURRENT, "MyFolder\\MyIndicator");
   if(h == INVALID_HANDLE)
     {
      Print("iCustom failed: ", GetLastError());   // 4802: no MQL5\Indicators\MyFolder\MyIndicator.ex5
      return(INIT_FAILED);
     }
   return(INIT_SUCCEEDED);
  }

Both compile in MetaEditor 5 with no errors or warnings. Adapt them to your EA; they were not run against a trade server.

Other MT5 errors

• MT5 error 4014: Function is not allowed for call
• MT5 error 4753: Position not found
• MT5 error 4756: Trade request sending failed
• MT5 error 4806: Requested data not found
• MT5 error 5004: File opening error
• MT5 error 10004: Requote
• MT5 error 10006: Request rejected
• MT5 retcode 10009: Request completed
• MT5 error 10013: Invalid request
• MT5 error 10014: Invalid volume in the request
• MT5 error 10015: Invalid price in the request
• MT5 error 10016: Invalid stops in the request
• MT5 error 10017: Trade is disabled
• MT5 error 10018: Market is closed
• MT5 error 10019: There is not enough money to complete the request
• MT5 error 10021: There are no quotes to process the request
• MT5 error 10022: Invalid order expiration date in the request
• MT5 error 10026: Autotrading disabled by server
• MT5 error 10027: Autotrading disabled by client terminal
• MT5 error 10030: Invalid order filling type
• MT5 error 10031: No connection with the trade server
• MT5 error 10044: The request is rejected, because the "Only position closing is allowed" rule is set for the symbol
• MT5 error 10046: The request is rejected, because the "Opposite positions on a single symbol are disabled" rule is set for the trading account.