What would make a bank withhold authorization for a purchase?

I ordered my textbook online (via SNHU's online bookstore) early, hoping to receive it just in time for class to start, or at least one to two days into the course (which is fine, as the first week is just introduction and whatnot, nothing heavy just yet). I waited and waited (and waited) in frustration, and my book never came (it had already been 17 days)! Come to find out that my order had been CANCELLED! So I ordered it again and had to wait for it to arrive (which was 3 and 1/2 weeks into the course). I had missed three very important homework assignments because of it. So I emailed the guys at the bookstore and they said that they never got authorization for the purchase, hence the cancellation of my order.

This has never happened to me before. It's the first time it ever happened. I've been using Visa for 11 years and have been banking with BoA for the same amount of years and in that time, that has never happened to me, not once. Why now!? Why me?