(1) After the period for rescission under RCW 26.26.330 has elapsed, a signatory of an acknowledgment or denial of paternity may commence a proceeding to challenge the acknowledgment or denial only:

     (a) On the basis of fraud, duress, or material mistake of fact; and

     (b) Within two years after the acknowledgment or denial is filed with the state registrar of vital statistics.

     (2) A party challenging an acknowledgment or denial of paternity has the burden of proof.

[2002 c 302 § 308.]