my guess would be the key, if the car is getting proper signals to open and close at least once all things can operate correctly.

if you lock, unlock, and then wait 10 minutes, can you lock again?

maybe if the battery in the remote is weak and having a hard time holding charge, its having a hard time charging up the capacitors that provide the energy for the signal pulse to be transmitted. or maybe the caps are on the way out too? good luck.