(a) After the period for rescission under W.S. 14-2-607 has expired, a signatory of an acknowledgment of paternity or denial of paternity may commence a proceeding to challenge the acknowledgment or denial only:
(i) On the basis of fraud, duress or material mistake of fact; and (ii) Within two (2) years after the acknowledgment or denial is filed with the state office of vital records.
(b) A party challenging an acknowledgment of paternity or denial of paternity has the burden of proof.