To dream that you forget or can't find where you parked your car indicates that you are dissatisfied or unhappy with an aspect of your waking life. You do not know what you really want to do with your life or where you want to go. To dream that your car has been stolen indicates that you are being stripped of your identity. This may relate to losing your job, a failed relationship, or some situation which has played a significant role in your identity and who you are as a person.
(This is on several.)