What was your mash thickness and grain bill? Did you leave it for an hour after stabilizing the temps, or just 45 minutes longer? By getting the grains to 160* you denatured a lot of the enzymes. There would still be enough left to finish conversion, but it would take some extra time, maybe even longer than 60 minutes. That right there could be your whole problem.
It could also be just a few small errors in measurments (temps which could effect hydrometer readings, larger volume than usual) that added up to make your efficeincy appear lower. Hell, if it's your first time brewing in a new place, it could even be that your process was a little different, which sent you screwey.