All grounds for relief available to an applicant under this act must be raised in his original, supplemental or amended application. Any ground finally adjudicated or not so raised, or knowingly, voluntarily and intelligently waived in the proceeding that resulted in the conviction or sentence or in any other proceeding the applicant has taken to secure relief may not be the basis for a subsequent application, unless the court finds a ground for relief asserted which for sufficient reason was not asserted or was inadequately raised in the original, supplemental, or amended application.