My sim was late for her carpool to work, so I clicked her car for her to drive herself. However, the game slightly froze for a second and my sim wasn't able to go to the car. She stomped her foot and the bubble above her head showed the footsteps with a line through it, indicating that she can't get to the car. But it's in its parking spot and not blocked by anything. So, I tried getting her a bike and the same thing happened. The bike and car are not blocked, so what's going on?
Try opening the cheat box (ctrl+shift+c) and typing in (resetSim *) without the parentheses and try again. If that doesn't work, try selling the old car/bicycle and buying a new one. There are always no end of path finding issues. Usually resetting Sims fixes those, though.