Check your owners manual books and look for a 4 digit code. You might have to enter that into your radio or (we have an '03 so I'm unfamiliar with the' 05) is thete a way to enter something using the stick left of the steering column or the buttons on the instrument cluster? The truck thinks it's been stolen. You need to enter the correct code to start the truck. Anti-theft?
Had your battery died and you changed the battery within a short time, this might not happen but for too long and the "reserve" batteries/capacitors on the boards of your 5 computers died too. Full reset. Call the bmw roadside assistance number.

I could also be dead wrong.

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'03 4.6is (the wife' s ride)