SS_OPTION_​ALLOW_PORT​_SAMPLE_TI​ME_IN_TRIG​SS

I'm using a For Each Subsystem and when I run the simulator it highlights a Simulink to Physical System Converter and reports the following error.

• Simulink-PS Converter/EVAL_KEY/EXEC_BLOCK' has port-based sample times and has_ been improperly placed in the iterator subsystem. Port based sample time S-Functions may only be used in iterator subsystems if they specify the option SS_OPTION_ALLOW_PORT_SAMPLE_TIME_IN_TRIGSS.

What does this mean?