What do you mean "the module operates"? Does the module run the fan when controlled locally at switch paddle? If so, something is interfering with the X10 signal on the powerlines. Usually a (new) electrical noise maker like a wall wart power supply (cell phone charger, cordless phone supply, computer, flat panel TV, etc.) Check for something new or something moved to a different outlet.
If the module does not respond to remote commands nor does it work at the switch, but yet fan runs when you jump around the switch, that sure sounds like a bad switch. Are you sure the other replacement modules were good?
