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MQL5 runtime error reference

MQL5 Error 4752: Trading by Expert Advisors prohibited

MQL5 error 4752 officially means "Trading by Expert Advisors prohibited." It is commonly captured from GetLastError when an EA attempts a trade while terminal or program permissions block automated trading. Enable the terminal Algo Trading control and the EA permission, then verify TERMINAL_TRADE_ALLOWED, MQL_TRADE_ALLOWED, and ACCOUNT_TRADE_EXPERT before submitting again. Capture GetLastError immediately around the failing call so an older error is not mistaken for the current failure.

Open MQL5 Coding AgentReview the diagnostic example

Open the Coding Agent and choose MQL5 from the language menu.

Isolate runtime error 4752.mq5
ResetLastError();
bool sent=OrderSend(request,result);
int runtime_error=GetLastError();

PrintFormat("sent=%s runtime=%d retcode=%u comment=%s",
            sent ? "true" : "false",
            runtime_error,
            result.retcode,
            result.comment);
  • Official meaning: Trading by Expert Advisors prohibited
  • Layer: terminal runtime
  • Read with: GetLastError
  • First step: isolate the failing call

Also searched as: mql5 ordersend error 4752.

Where error 4752 comes from

It is commonly captured from GetLastError when an EA attempts a trade while terminal or program permissions block automated trading. The numeric value is listed in the official runtime error table, which is separate from MetaEditor compilation errors and trade server return codes.

Reset the last-error state before the suspected call, save its direct return value, and read GetLastError immediately afterward. This produces a causal log instead of a stale code.

Checks that narrow the cause

Preserve the exact parameters and terminal context that produced the failure. Check one precondition at a time before adding retries.

  • Read TERMINAL_TRADE_ALLOWED for the client terminal.
  • Read MQL_TRADE_ALLOWED for the running EA.
  • Read ACCOUNT_TRADE_EXPERT for the logged-in account.
  • If a request reaches the server, inspect MqlTradeResult.retcode separately.

Apply the smallest repair

Enable the terminal Algo Trading control and the EA permission, then verify TERMINAL_TRADE_ALLOWED, MQL_TRADE_ALLOWED, and ACCOUNT_TRADE_EXPERT before submitting again.

After the repair, test both the expected path and a deliberately invalid input. The second test confirms that the diagnostic branch still exposes failures.

Use a focused diagnostic

The log keeps runtime error 4752 separate from trade server retcodes such as 10027. That distinction tells you which permission layer rejected the operation.

A clean compile or a cleared error code does not prove strategy logic, broker compatibility, backtest quality, or live-trading safety. Reproduce the result in the target MetaTrader 5 terminal and account environment.

Isolate runtime error 4752.mq5
ResetLastError();
bool sent=OrderSend(request,result);
int runtime_error=GetLastError();

PrintFormat("sent=%s runtime=%d retcode=%u comment=%s",
            sent ? "true" : "false",
            runtime_error,
            result.retcode,
            result.comment);
Where Pineify fits

Repair editable MQL5 source with compiler feedback

Pineify can generate or revise MQL5 source and use MQL5 compilation diagnostics during the coding workflow. Keep the exact error, source location, program type, and intended behavior in the request so the change remains reviewable.

Open MQL5 Coding Agent

Pineify does not run your broker terminal, Strategy Tester, market data, or live orders. Validate the final program in your own MetaTrader 5 environment.

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A practical verification workflow

  1. 1

    Reset the error state

    Call ResetLastError directly before the suspected function so the next code belongs to that operation.

  2. 2

    Record call and inputs

    Save the function return value, every input, and GetLastError. Confirm that the captured runtime code is 4752.

  3. 3

    Validate the preconditions

    Read TERMINAL_TRADE_ALLOWED for the client terminal. Read MQL_TRADE_ALLOWED for the running EA. Read ACCOUNT_TRADE_EXPERT for the logged-in account. If a request reaches the server, inspect MqlTradeResult.retcode separately.

  4. 4

    Retest in the target terminal

    Compile the changed source, repeat the failing operation, and test the surrounding EA or indicator behavior in MetaTrader 5.

Frequently asked questions

What does MQL5 error 4752 mean?

The official runtime error table defines 4752 as "Trading by Expert Advisors prohibited."

Is error 4752 a compiler error?

No in this context. It is a terminal runtime code. Compiler diagnostics and MqlTradeResult.retcode values use separate code tables.

Why should I call ResetLastError first?

The terminal stores the last runtime error. Resetting it before the suspected call makes the following GetLastError value easier to attribute to that call.

Last verified against the linked official references on . Compile and test the final source in the MetaTrader 5 build, broker, symbol, and account environment you plan to use.

Continue with reviewable MQL5 source

Provide the exact diagnostic and intended behavior, inspect the generated change, compile it, and verify it in your MT5 test environment.

Open MQL5 Coding Agent