Problem with X10 Switch

Today, I installed two X10 light switches, so that we can easily control some of our lights. I had attempted this before, and am running into the same problem I had before. I can’t readily explain why it happens, but it’s easy enough to explain the symptom: using X10, I can turn the light on, but I can’t get it to respond to the light off signal. There is one odd thing about this light: this is the light over our front door and garage door, and our landscape lights. There are special X10 accessories for low voltage products, but these landscape lights go through a transformer, so they should be standard 120V devices as far as X10 is concerned.