Ok as weird as this sounds, if you are having the same problem, try this:
Before turning your screen on, shine a flashlight at the photosensor for about 10 seconds, then give it power... Mine seems to work every time like that.
The screen seemed to work less often in the morning when I get out of work, and lately (as the sun sets sooner) when I go to work. Any time it is dark out, the problem seems random, but rarely ever in the day.
Now Xenarc just needs to supply flashlights with all their 706 screens.....