Yep, I have two 300W halogens, one that is infinately variable and one that has two levels. The lamp modules work fine on the two step version, but the dimmer circuit confuses X-10 controller, it ends up giving eratic brightness, and sometimes doesn't respond.

Not sure why, I suspect that they use the same type of chopping to dim the light, so the dimmer in the lamp doesn't function correctly.

If you turn the light on full the X-10 dimmer seem to work just fine (on my lamp anyway).

DK