ARTICLE: CIA base attacked in Afghanistan supported airstrikes against al-Qaeda, Taliban, By Joby Warrick and Pamela Constable, Washington Post, January 1, 2010

Would appear, at first glance, that this would be the major reason for the attack.

Inevitable, when you think of it: drones becoming so big, CIA being so big in their deployment, ergo CIA becomes target of retaliation for their successful employment.

Like most things, these attacks get interpreted as a "major setback" when--most often--they represent friction in response to serious advance on our part. You want no friction, you avoid any movement, but if you move forward, don't expect anything but more friction.