recompilation results in indicator/EA not loading

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I have reinstalled MT5/MQL5.

MetaTrader 5, Version 5.00, build 5488. Date: 19th December 2025


I have copied my old indicators to the new installation directories. Its weird this!


I can load old FSI_v7.ex5 but if I recompile it it won't load giving error:

2025.12.22 05:38:34.246 Custom Indicator loading of FSI_v7 (NZDUSD,H1) from C:\Users\bapo_\AppData\Roaming\MetaQuotes\Terminal\D0E8209F77C8CF37AD8BF550E51FF075\MQL5\Indicators\PipReaper\FSI_v7\FSI_v7.ex5 failed [539]


original load before recompilation:

2025.12.22 05:35:48.095 Indicators custom indicator FSI_v7 (AUDCAD,M15) loaded succesfully

2025.12.22 05:35:48.102 Indicators custom indicator FSI_v7 (AUDCAD,H1) loaded succesfully

2025.12.22 05:35:48.102 Indicators custom indicator Custom_ATR (AUDCAD,H1) loaded succesfully

2025.12.22 05:35:48.795 Indicators custom indicator FSI_v7 (AUDCHF,M15) loaded succesfully

2025.12.22 05:35:48.798 Indicators custom indicator FSI_v7 (AUDCHF,H1) loaded succesfully

2025.12.22 05:35:48.799 Indicators custom indicator Custom_ATR (AUDCHF,H1) loaded succesfully

2025.12.22 05:35:48.803 Indicators custom indicator FSI_v7 (AUDJPY,M15) loaded succesfully

2025.12.22 05:35:48.807 Indicators custom indicator FSI_v7 (AUDJPY,H1) loaded succesfully

2025.12.22 05:35:48.807 Indicators custom indicator Custom_ATR (AUDJPY,H1) loaded succesfully

2025.12.22 05:35:52.852 Indicators custom indicator FSI_v7 (AUDNZD,M15) loaded succesfully

2025.12.22 05:35:52.855 Indicators custom indicator FSI_v7 (AUDNZD,H1) loaded succesfully

2025.12.22 05:35:52.855 Indicators custom indicator Custom_ATR (AUDNZD,H1) loaded succesfully

2025.12.22 05:35:52.857 Indicators custom indicator FSI_v7 (AUDUSD,M15) loaded succesfully

//+------------------------------------------------------------------+
//|                                                         test.mq5 |
//|                                  Copyright 2025, MetaQuotes Ltd. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2025, MetaQuotes Ltd."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property indicator_chart_window
#property indicator_buffers 1
#property indicator_plots   1
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
  {
//--- indicator buffers mapping
   
//---
   return(INIT_SUCCEEDED);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int OnCalculate(const int32_t rates_total,
                const int32_t prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int32_t &spread[])
  {
//---
   
//--- return value of prev_calculated for next call
   return(rates_total);
  }
//+------------------------------------------------------------------+

The above code produces the following error: 

2025.12.22 06:14:37.351    Custom Indicator    loading of test (NZDUSD,H1) from C:\Users\bapo_\AppData\Roaming\MetaQuotes\Terminal\D0E8209F77C8CF37AD8BF550E51FF075\MQL5\Indicators\test.ex5 failed [539]

Interestingly if I substitute the above code with Accelerator.mq5 contents it compiles and loads normally as the Alligator indicator.

Step on New Rails: Custom Indicators in MQL5
Step on New Rails: Custom Indicators in MQL5
  • 2009.11.23
  • www.mql5.com
I will not list all of the new possibilities and features of the new terminal and language. They are numerous, and some novelties are worth the discussion in a separate article. Also there is no code here, written with object-oriented programming, it is a too serous topic to be simply mentioned in a context as additional advantages for developers. In this article we will consider the indicators, their structure, drawing, types and their programming details, as compared to MQL4. I hope that this article will be useful both for beginners and experienced developers, maybe some of them will find something new.
 
rob:

I have reinstalled MT5/MQL5.

MetaTrader 5, Version 5.00, build 5488. Date: 19th December 2025


I have copied my old indicators to the new installation directories. Its weird this!


I can load old FSI_v7.ex5 but if I recompile it it won't load giving error:

2025.12.22 05:38:34.246 Custom Indicator loading of FSI_v7 (NZDUSD,H1) from C:\Users\bapo_\AppData\Roaming\MetaQuotes\Terminal\D0E8209F77C8CF37AD8BF550E51FF075\MQL5\Indicators\PipReaper\FSI_v7\FSI_v7.ex5 failed [539]


original load before recompilation:

2025.12.22 05:35:48.095 Indicators custom indicator FSI_v7 (AUDCAD,M15) loaded succesfully

2025.12.22 05:35:48.102 Indicators custom indicator FSI_v7 (AUDCAD,H1) loaded succesfully

2025.12.22 05:35:48.102 Indicators custom indicator Custom_ATR (AUDCAD,H1) loaded succesfully

2025.12.22 05:35:48.795 Indicators custom indicator FSI_v7 (AUDCHF,M15) loaded succesfully

2025.12.22 05:35:48.798 Indicators custom indicator FSI_v7 (AUDCHF,H1) loaded succesfully

2025.12.22 05:35:48.799 Indicators custom indicator Custom_ATR (AUDCHF,H1) loaded succesfully

2025.12.22 05:35:48.803 Indicators custom indicator FSI_v7 (AUDJPY,M15) loaded succesfully

2025.12.22 05:35:48.807 Indicators custom indicator FSI_v7 (AUDJPY,H1) loaded succesfully

2025.12.22 05:35:48.807 Indicators custom indicator Custom_ATR (AUDJPY,H1) loaded succesfully

2025.12.22 05:35:52.852 Indicators custom indicator FSI_v7 (AUDNZD,M15) loaded succesfully

2025.12.22 05:35:52.855 Indicators custom indicator FSI_v7 (AUDNZD,H1) loaded succesfully

2025.12.22 05:35:52.855 Indicators custom indicator Custom_ATR (AUDNZD,H1) loaded succesfully

2025.12.22 05:35:52.857 Indicators custom indicator FSI_v7 (AUDUSD,M15) loaded succesfully

The above code produces the following error: 

2025.12.22 06:14:37.351    Custom Indicator    loading of test (NZDUSD,H1) from C:\Users\bapo_\AppData\Roaming\MetaQuotes\Terminal\D0E8209F77C8CF37AD8BF550E51FF075\MQL5\Indicators\test.ex5 failed [539]

Interestingly if I substitute the above code with Accelerator.mq5 contents it compiles and loads normally as the Alligator indicator.

You need to run your MetaTrader in the portable mode - that's to start with.

To use this mode, start the platform from the command line with the additional /portable key. For example, "C:\Program Files\MyTerminal\terminal.exe /portable"

https://www.metatrader5.com/en/terminal/help/start_advanced/start

Platform Start - For Advanced Users - Getting Started - MetaTrader 5 Help
Platform Start - For Advanced Users - Getting Started - MetaTrader 5 Help
  • www.metatrader5.com
After installation, a group of programs of the trading platform is added to the Start menu, and the program shortcut is created on the desktop. Use...
 

Thanks.

Thats pushed me forward.


Now all I need to do is redevlop my indicator into full compliance with the new strict rules introduced in this build it seems.

 
rob:
2025.12.22 06:14:37.351    Custom Indicator    loading of test (NZDUSD,H1) from C:\Users\bapo_\AppData\Roaming\MetaQuotes\Terminal\D0E8209F77C8CF37AD8BF550E51FF075\MQL5\Indicators\test.ex5 failed [539]

Ошибки, баги, вопросы

Alain Verleyen, 2025.12.19 14:47

Confirmed and reported to MQ.

Thank you.

 

I experienced exactly same problem:

On MetaTrader 5 build 5488, any newly compiled custom indicator fails to load with error [539], even when the indicator is a trivial baseline.
Previously compiled EX5 indicators continue to load normally in the same terminal.  Blocks development of all new custom indicators, as any newly compiled EX5 cannot be loaded.

 

Don't use beta build if you don't want to be beta-tester.

https://www.mql5.com/en/forum/502088

All about MT5 updates.
All about MT5 updates.
  • 2025.12.16
  • www.mql5.com
This topic will be used to bring together all information about MT5 updates process. This is NOT for chitchat...
 

I’m getting the same issue on build 5488. Any new custom indicator even the default ones stops working after compiling and shows a failure [539].

I also don’t think this is a beta version, since I updated it directly through the official MT5 popup. I’ve tried reinstalling it multiple times using the main download link from the MT5 website, but it always installs the same version.

The problem occurs on both Windows 11 and Windows 10, and I’ve tested it on multiple PCs. The only machine that still works correctly is a Linux system running build 5480.

It would be great to have access to download older versions of the software, especially when new updates are broken like this.

 
miguellvds #:

I’m getting the same issue on build 5488.is.

5430 is the latest "release" version.
 
miguellvds #:

I’m getting the same issue on build 5488. Any new custom indicator even the default ones stops working after compiling and shows a failure [539].

I also don’t think this is a beta version, since I updated it directly through the official MT5 popup. I’ve tried reinstalling it multiple times using the main download link from the MT5 website, but it always installs the same version.

The problem occurs on both Windows 11 and Windows 10, and I’ve tested it on multiple PCs. The only machine that still works correctly is a Linux system running build 5480.

It would be great to have access to download older versions of the software, especially when new updates are broken like this.

Please read what is posted.
 
Same here. Can’t load any New Indicator after updating to beta. Normally we encounter issue like this but this is annoying. Can old previous indicator but newly compiled indicator won’t even attach to chart and trying to brute apply by ChartIndicatorAdd we get Error 5802. Hmm. 
 
Did anyone solved this 539 error?? I'm getting this error even if I create a new indicator from the editor. Please help. Nothing is working - not beta release, not stable release, not the /portable argument.
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