same year here, someone else also has had the problem and it was also an 08...

http://www.xoutpost.com/bmw-sav-foru...tely-dark.html

no resolution so far... got the latest firmware and after that it still happened on 2 mornings (not cold, and also garaged). Still random, still don't know the root cause for sure.

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr