"Bishop" Williamson was made a Bishop but the late Bishop Lefebvre WITHOUT permission of the Vatican. While the Catholic Church upholds the act that made Williamson a bishop, the Vatican also said it was an act of Schism with the Vatican and ex-communicated him for it. This is the Excommunication Benedict XVI has removed. Furthermore Williamson is NOT viewed as a Valid Bishop of the Catholic Church do to his advancement to being a Bishop was NOT approved by the Vatican. That later status was NOT changed by the lifting of the excommunication (i.e. he is still NOT a Bishop within the Catholic Church).
http://en.wikipedia.org/wiki/Richard_Williamson_(bishop)
http://www.google.com/hostednews/ap/article/ALeqM5gpbkisgs-EZ40shoCodJd4rfBNwAD95V35RO0One of the problem of Benedict XVI is he wants the Pius X society back within the Catholic Church, not because he wants the membership but he dislikes schism and will try to work to get such schismatic groups back within the Church.
Please note, Benedict is worried about Schismatic groups i.e. Catholic Groups that broke from the Vatican for reason other then dogma. Protestants are NOT viewed as Schismatic Catholic Groups but as separate Christian Religions, and thus part of Benedict's efforts to bring SCHISMATIC Catholics back into the Church. The two largest groups are dissenters from Vatican I (1860s)and Vatican II (1960s). The 1860s dissenters viewed Vatican I as giving to much power to the Vatican, while Vatican II dissenters object to the reforms of Vatican II, including non-latin masses, adopting of Religious freedom instead of the traditional Catholic rule of Religious toleration, the Pius X group even oppose the limited increase in the number and power of Women within the Church since Vatican II.
Benedict XVI is trying to get the Pius X Society back within the church, but also trying to get them to embrace the reforms of Vatican II. John Paul II saw this as impossible and excommunicated the lot, but Benedict XVI thinks he can get them back in without having to give in on any of the reforms of Vatican II. I believe Benedict XVI is wrong, and he will fail, but he is trying to show he will work with the Pius X group if they will work with him. The Holocaust Denial by Williamson is NOT helping the Situation, the Vatican accepts that the Holocaust took place and it was bad, why Williamson wants to deny it seems to be Williamson's choice.
As I said above Benedict is trying to get as many groups that have broken away from the Catholic Church do to changes adopted in Vatican I and Vatican II back into the Catholic Church, I see him failing. These right wing radicals view the limited reforms of Vatican II as to radical and will only return to the Catholic Church when the reforms are dropped. Benedict XVI (as was John Paul II) a young man involved in Vatican II and can not and will not change Vatican II, but at the same time Benedict XVI wants as many schismatic groups back into the Church as he can get. Thus Benedict's lifting of the Excommunications to show he is willing to work with the Pius X society and other groups without preconditions. Unfortunately I believe the Pius X Society will NOT deal with anyone who embraces Vatican II, thus this is a doom effort by Benedict XVI.