It is a problem, usually, with the photo sensor in the hud itself. There is a fix. You have to pull the hud out and re-solder the photo sensor to the board. I know there is a write up on that somewhere. I may have it on my PC at home. Its not terribly difficult as long as you know how to solder.

That said, make sure your brightness control is all the way up on the dimmer on the dash. I have never heard of any problems with that switch but its always a possibility.