Section 26.26A.240 - Challenge after expiration of period for rescission(1) After the period for rescission under RCW 26.26A.235 expires, but not later than four years after the effective date under RCW 26.26A.215 of an acknowledgment of parentage or denial of parentage, a signatory of the acknowledgment or denial may commence a proceeding to challenge the acknowledgment or denial, including a challenge brought under RCW 26.26A.465, only on the basis of fraud, duress, or material mistake of fact.(2) A challenge to an acknowledgment of parentage or denial of parentage by an individual who was not a signatory to the acknowledgment or denial is governed by RCW 26.26A.445.