Thanks for the suggestions and encouragement, everyone. I suspect you've all hit on a part of the real answer!
Shannon - it's true that my muscles usually feel a bit stiff or sore from the workouts, so they may be holding some water.
Choirgirl - yes, I've been telling myself all along that I wouldn't be able to keep up a 2 lb/wk loss all the way to goal, so maybe the timing of the slowdown is just coincidence.
midwife - muscles would be good!
n I think I have probably at least slowed the muscle loss I must have been having before I started lifting, and hopefully gained a bit. No, I haven't had my bodyfat checked because my fitness club is a rather bare bones one and doesn't offer that service. Their "trainers" are nearly all students who encourage push low-weight, high-rep, machine workouts. It was a good choice for me when I first started losing weight, in that it was non-intimidating, not expensive, and close to home. I would never have been brave enough to walk into most of the other gyms! I've outgrown it, and as soon as I can I'll be looking for a new gym, but for now I'm pretty much on my own.
beerab - yes, it may well be just a normal slowdown (not even really a plateau, because I am still losing slowly), so I'll try to be patient!
sportmom - I did reduce the cardio for the first 3 weeks, because NRLW says endurance cardio (vs. intervals) is optional. Then I realized that I wasn't losing and have cranked up the cardio levels again.
I'm supposed to take a recovery week between stages of the program, so I won't be lifting this week. It will be interesting to see what happens on the scale. The thing I'm proudest of is that I am frustrated but I'm not discouraged. Any other time I've tried to lose weight I would have given up by now, but this time I'm sticking with it and eventually it will work.