Did you do the entire procedure?
Link to another post with instructions:
http://bimmerfest.com/forums/showthread.php?t=8043
1) Get in and close all doors.
2) Turn on the ingition and turn off quickly. (No more than 5 seconds) to start the process. Next action must take place within 30 seconds.
3) Remove the 1st key.
4) Hold the key up near your left shoulder (this is so it is closer to the remote reciever antenna - someone else suggested this).
5) Hold down the unlock button (which is button 1 on my key) and press the lock button 3 times (center button on my key). Release the unlock button and the doors lock which confirms the operation.
6) Quickly repeat steps 4 & 5 for key #2 etc.
If it does not work, try doing the keys in opposite order. Key 2 then key1, vs 1 then 2.
Do you have several keys? You have to reinitialize them all, quickly.
I have three masters and the order in which I program them might matter. You may want to try the procedure using key #1 then key #2, and if that does not work, key #2 then key #1...
Why did you have to initialize the keys in the first place? Did you get a new one? Did you change batteries?
How old or what condition is your vehicle battery?
How is the condition of your key batteries? (Any time you post tech questions, year of the car -along with model and in some cases, miles- is helpful.) If your car is a year that had replacement batteries in the key, it's best to start with all new batteries.
Which one does yours look like?