Undefined identifier when using LibMdlStartCustomCode

Hi,

I'm using the function LibMdlStartCustomCode in a tlc file:

%<LibMdlStartCustomCode("aaa","trailer")>

However, I obtain the following error message at code generation:

Error: File: C:\Program Files\MATLAB\R2021b\rtw\c\tlc\mw\hookslib.tlc Line: 320 Column: 22
Undefined identifier System
Main program:
==> [00] C:\Program Files\MATLAB\R2021b\rtw\c\tlc\mw\hookslib.tlc:LibMdlStartCustomCode(320)

do anyone have an idea what is going on ?