Hmmmm. I think I've got it. Two Seperate Circuits. One is a normal dimmer to a single halogen, which works OK, proving that the halogens can be dimmed. (Typing this for MY benefit...) The second has both an identical halogen and an incandescent.
This worked for a while and then stopped. A simple question, does the switch respond to ANY commands. (I.E. dim, bright, etc?) I, (unfortunately) would lean twards bad switch, if there is NO response, unless the X-10 PLC signals are getting sucked up or blocked in some way. Do you have ANY other X-10 modules to verify the operation of basic X-10 signals? Is this switch on the same phase as the X-10 device sending the PLC signals, and has anything been added or moved?
Lots of questions, I Know, but for me, at this point, it comes down to checking everything, a step at a time, to see where the problem lies.
Hope this info is of some help.