[Trevikins]

I've had this problem on two occasions and had to call BMW Emergency Services out both times. The first time the guy checked the relay and couldn't find a fault, however when he put it all back together it worked fine. The second time (exactly 12 months after the first incident) the guy did what he called a reboot and it worked fine. He advised that it was probably software related and that I should ask for a software update at the next service.

The car is due in within the next month or so, but in the meantime I keep the windcreen coated in rain repellant just in case.

Hope this helps.

EDIT: forgot to add that mine is a December 2010 build.