Just experienced the same issue. I replaced the battery because it tested bad. No problems since. If it's the original battery, it's time for a replacement.

Actually, battery is brand new and charging system tested ok. Like I said, the diagnostic threw a code for the Integrated Power suppy Module.

Anti-Theft module - $185
ECM Control Unit - $1500
Starter - $440

I could not find the IVM. If you have a part number, I would look it up.

I wanted to give everyone an update:

My mechanic (non-bmw) recommended we have the truck diagnosed and he called one of those mobile diagnostic services that come to your place and do a diagnositc on your car. The guy worked on the truck for 1 1/2 hours (luckily the truck was not starting so they got to see first hand what was going on).

Finally, they found out it was the IVM Module which is apparently located in the engine compartment. Now, I don't know if this is the whole ECM or a separate module which apparently controls the electronics of the X5 (forgive me as I didn't speak to the tech first hand). Anyway, once they bypassed that module, the truck started right up. On Monday, the module was replaced and the truck has been starting consistantly ever since.

Since this is my friend, he released the car to my wife w/o payment so I'll be visiting him on Saturday to get the invoice. Once I get it, I can give you all the part # for the module that was changed.

I just wanted everyone to know that the reason my X5 wouldn't start was a faulty Integrated Power Supply. The part # is 12527510638 and it costs about $125.

Hey tomsawyer, do you have a 4.4? I have been experiencing similar symptoms in which my 3.0 will only engage the starter and then start on the 2nd or 3rd key turn. However, when I looked up the part # you referenced, it appears to only apply to the 8 cyl X5s. Trying to figure out what my problem might be. Thanks-

Update????????

Mine does the same every few months. Good to know what to check when it does it more often. Thanks for the answer to a future problem.

Is this a 3.0 issue only??