...I can turn it on and off with the "On-Off" Icon.
Are you turning it on then off right away to verify it works? If so, wait a minute after turning it on, then try turning it off with the icon. It's not that common, but depending on the wattage of the bulb and the
electrical distance from the
CM15A to the
switch, if the line & load wires of the switch are reversed the extra resistance of the hot bulb filament can degrade the X10 signal to the point where it's to weak for the switch to recognize. If the line & load wires are reversed, the switch will still work properly but the X10 signal has to pass thru the load (light bulb) on it's way to the switch.
I also have a timer associated with it that turns it ON when it's supposed to but will not turn it OFF when it's supposed to.
If the above is not the problem, and you double checked the off time of the timer
, then the problem could be that something else is getting powered on before the off command gets sent and it's causing interference or signal degradation.