I've got a similar switch and I was able to program it with a palm pad through an MR26A connected to HS.
When the switch sees ANY X10 command on the line it should blink the green always-on LED on top, even if it doesn't respond to the command. If you don't see this happening, I'd bet the X10 signal or command isn't getting there, or the switch is not wired correctly, or it's bad. Try sending it a default code just in case it's not getting the program code you expect.
Also, if you have any other devices sending codes, such as motion sensors, the switch might be getting another code before you can send it the right code from the palm pad.
There was a report a while back that some palmpads didn't always send the proper code for some devices. I don't recall if it was the model you mentioned or not. You might want to try another device to send the code, such as a plug-in controller.