The believe that Pope John XXIII had dabled in masonry before his election. Therefore he was automatically excommunicated. They claim his excommunication invalidated his papal election.
There is no proof he had dabled in masonry.
Even if he had, canon law at the time (and still today) holds that papal elections of those excommunicated are valid, and their election immediately removes the excommunication.
Because his election was invalid, all subsequent elections are invalid but the now the electorate is invalid.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.