Problem solved.
If someone is facing the same problem, in newer versions of ngx-bootstrap the arguments required doesn′t need the initialParent anymore:
I just had to put it in this way:
this.bsModalRef = this.modalService.show(RegisterEnterpriseComponent);
And it works without any problems.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…