Just got my 2000 M5. The keyless entry unlocks properly, the trunk button works and the windows will go down via remote but it will not lock from the remote. I can do it with the key and the alarm beeps OK.

Is this car one of those that will not lock the keys in the car by sensing where the key is? I just got the car and only have the one key, is it possible the other one is in the car somewhere and thus preventing it from locking??? This sounds pretty far fetched and it would just be too perfect if the other key was in the car (probably $100+ from BMW I suppose.)

the e39 m5 doesnt have the feature you are talking about, you can lock the key inside the car noproblem. try reprogramming the key

http://www.techbmw.com/forums/showthread.php?t=9

Thanks for the link. A ways down into the text is a statement regarding key battery voltage. Apparently, if the voltage is between 2.2 and 2.6 volts, the car will unlock but not lock - VIOLA!! Time for a new battery.

your key is molded around the battery, you'll have to order a new key or open the one and glue it back together.