Could be one of two things:
Interference -- shield your CarPC better and look for loose connections and looped wires. Test this by using the keyfob at various distances from the car. Also, it would be nice to know where the receiver is, so you could aim towards it and see if it helps.
Smart Car -- your car detects a load on the electrical system and it won't let you lock it up, forcing you to ensure you haven't left the headlights on.
Oh yeah, check the batteries on the keyfob as well...