I'm having the same problem also. Do you have the BMW alarm system installed? I had mine at the dealer for two days hooked up to a computer connected to BMW Munich, for software update related to this problem. It worked great for a week, then back to the some old thing.
Every model the Bavarian brand produces is an engineering masterwork, manna for driving enthusiast, an internal-combustion mallet for pummeling comparison-test rivals into humiliated awe - Arthur St. Antoine