From reading the AB forum and talking to a friend on the volunteer staff it appears that most of it boils down to two problems. 1) They were denied space at the Sheraton this year, where they usually have a few spillover events and do the registrations, so they were forced to improvise in an unfamiliar space; and 2) they were using a new semi-selfserve registration system that they had not adequately tested. When one (or was it two?) of the card printers broke and it became clear that it took much longer for attendants to self-register than they had planned, they did not have any kind of back up plan, like say pen and paper, to put in place.

The AB Director of Registration has written a formal statement here. I haven’t read it yet so she may contradict what I’ve written above.