It means that the MT's module for communication with the trading server is off. It can be overloaded or crashed.

You can try the following:
- switch off all experts.
- Press F3 to see the MT's "Global Variables" screen.
- Delete all stored records.
- Restart MT.

Try again. It must be ok.

Hans,
My screenshot above is from live trading with a MT Expert Advisor.

Oh, that's true, sorry. Then I don't know what the problem is with my EA. I don't get any related errors in the Expert tab. Only The following Errors of other EA's:

Hans, you strategy has 17 indicator + logical groups!! How are you sure what exactly indicator makes the problem?

That's the only indicator I'm sure doesn't work in live trading. That's why I said that the Osc of MACD may not be the only one, but the only one I'm sure doesn't work. I know that because "Close out long position" was true and it didn't close out the long position.

Again, live trading and the MT4 backtester are not the same thing. That's why I said it does work in the MT4 backtest (what you did), but doesn't work in actual live trading (EA, not bridge).

I'll try that, although this is separate from the Indicator bug.

And I didn't want to be offensive. Just wanted to point out a bug. I don't see how I implied that you develop software to help steal the traders money. I'm grateful for all the work you do.

If you want to study the behavior of one indicator, the best is to use only that indicator in the corresponding role.
In your case the "Oscillator of MACD" indicator is used as a closing condition.

I made a simple strategy that opens only long positions and uses  "Oscillator of MACD" for closing. I'm using the same parameters as yours.

It closes the positions successfully:

From my experiment I see that the indicators works well, so the problem must be other.

I see you use Day Closing indicator for closing point. This indicator detects the expected bar close for the day and sends a close signal 15 seconds earlier. However, if there are no ticks in that period, the indicator is not able to work. I suggest you to use Day Closing 2 indicator and to set closing time at least 1 minute earlier than the market close hour for the week days and Friday.

...
I'll edit the header of your topic because it is misleading ind offensive. We do not develop software for brokers to help them stealing the traders money.