I want to leave this as a contribution to the community.
I have found that the macro sc_ajax_message(); does not work on an Ajax button in scriptcase, so I have dedicated hours to solve the problem.
I only ask you to comment if it has served you.
What happens is that PHP7.1 > = gives error when variables type array are not correctly defined.
You should only add this line before using the macros sc_ajax_message(); and that's it.
$this->NM_ajax_info['ajaxMessage']=[];
Comment to find out if it's worthwhile to share this.