David Bawden (aka pope Michael) claims to be the successor to pope Pius XII (link to story). Like many folks, Mr. Bawden recognizes that modern Catholicism (post Vatican II) represents a break with more traditional Roman Catholic beliefs. In the quotations provided in the article, Mr. Bawden points to an alleged change in the view of the atonement from essentially a limited atonement view to a general atonement view. He apparently broke away from the Society of Saint Pius X (SSPX) back in the 70's and in 1990 was elected to the papacy (apparently by six of his followers). According to the article, he excommunicated pope John Paul II, though the article doesn't indicate what action (if any) he has taken toward Benedict XVI.
I wouldn't be surprised if Rome's devoted children soon tell us that this (like so many disputes over the papacy over the years - including the new splinter formed by pope Michael's former follower Teresa Stanfill Benns) is the result of Sola Scriptura. Don't ask me how that is supposed to be logical, since these groups probably think that Rome is to accommodating toward Sola Scriptura. But if Roman apologists can blame Sola Scriptura for Mormonism, (so-called) Jehovah's Witnesses, Oneness Pentecostalism, and so forth, they cannot reasonably draw the line at the variant versions of their own religion.