Problem With My Unicorn Model 120 Stairlift?

Earlier this week, after my mother-in-law rode her stairlift to the top of the stairs, an F6 error code is being displayed. I checked the owners manual and it says the chair went past the sensor at the top of the stairs. It says to manually crank the chair down past the sensor, and turn the chair on and off. I did this and the error is still being displayed. Does anyone have any suggestions? I called a technician from Unicorn, and they want $195 just to come out to the house.