Happened to my e70 2 days ago when it got a few degrees below freezing. Restart fixed it but only after a few tries wen the car was warmed up properly.

It used to happen to my e65 too whenever it got very cold. Dealer was not able to fix it. They put in a new screen and it happened again.

I figure it's probably something to do with the "liquid" in the display getting too cold.