Maybe re-programming it may help. These instructions include how to clear a transmitter current memory and reprogram it. I can email you the full instructions and a copy of the Owner's Manual, but here's the part I'm referring to. I couldn't figure out how to attach the .pdf files here.

"To clear a lost or stolen transmitter from the system's memory, program a transmitter four (4) times. This will remove the missing transmitter from memory since only four (4) transmitter codes can be accepted.

Another way to clear a lost of stolen transmitter is to erase all transmitter codes and then reprogram them. Refer to the security system owner's manual."