I had the same thing happen this weekend. It had to do with me taking my headlight apart and not putting it back together properly. If the seal isn't air tight, you will get condensation inside the lens.bimmee said:
If you or the dealer hasn't messed with the headlight, I would have them check your seals. There is a rubber boot on the back of the headlamp assembly, and another rubber seal around the whole plastic lens.