Jesuit Father Edward T. Oakes, a Mundelein Seminary Theology professor explains Pope Benedict's VERY clear reasons for putting to bed the ex communications of the SSPX bishops while delving into the acceptance of (or not) "Vatican II theology." What Vatican II said is a bone of contention of many, for a very long time....
You've got to read the article, Benedict's Vatican II Hermeneutic in First Things!