16If any person aggrieved by an improvement order or by an order varying or revoking an improvement order desires to question its validity on the ground that it is not within the powers of this Act or that any requirement of this Act has not been complied with, he may within six weeks from the date of the first publication of the notice referred to in sub-paragraph (b) of the last foregoing paragraph make an application for the purpose to the Court of Session, and if any such application is duly made the Court, if satisfied that the order is not within the powers of this Act or that the interests of the applicant have been substantially prejudiced by a failure to comply with any requirement of this Act, may quash the order either generally or in so far as it affects any property of the applicant; but except as aforesaid the order shall not at any time be questioned in any proceedings whatsoever.