Transmission Car will not Move in reverse

My car has 170,000 on it I change transmission oil &filter every year no sludge or patricals in the pan, no burning smell(clean). Last change was 9/25/10. OBD Code problem with throttle position sensor A circuit, dispite this code(on for over 2 years)never had a problem driving.I wanted to upgrade the security in the car for my wife so a new alarm system with remote start was installed 3 weeks ago, it was working fine, I took it back to have the trunk relese added to the system 11/21/10 I then installed new throttle sensor 11/22/10 drove home with no problem. My wife then drove to a shoping mall 11miles from home parked, and when she came out the car would not reverse.I installed the old sensor on the spot, you could see/feel the tranny take reverse but car would Not Move. Iput the new sensor back in, pushed car out of the stall and drove home with car shifting normaly. It still will not move in reverse.I need some info before going into a tranny shop. Thank you Frank Peters-Smith.
Can something electrial cause the tranny to lock up and not take reverse. #516-665-8858