Hello lponcho!
Welcome to the forums! I think I can help you with this. I've had to unlock my radio a time or two due to a dead battery. The process is simple, but tricky at the same time.
You only have 3 chances to enter the correct code, otherwise you must wait before entering it again for a minimum of 2 hours. The thing about these two hours is that the car ahs to be started. I will go into more detail below on this..
Unlocking radio:
1. Turn on car and then turn on radio
2. Enter the numbers in the exact order as you see them.
3. If you hear a beep noise before you have finished entering the code, then immediately start over entering the numbers from the beginning. (ex if your code is 12345 and you hear a beep on the third digit then it should look like this.. [1][2][3]*beep*[1][2][3][4][5]-->finished)
4. If you have entered the unlock code more than 3 times (which is the temporary limit) then you must wait for a while. It is part of the design for the anti-theft feature. Continue on below if you have entered the number more than 3 times.
Waiting for 2 hours before entering the code again:
1. This is very hard to do, but just turn off your radio and drive your car for 2.5 hours just to play it safe. Now I'm not sure if this time has to be all straight at once or if it can be stread out by driving someone then driving back, but you can try either. Just remember that if you touch any keys within this 2-2.5 hour period that the timer will reset and you will be forced to wait another two hours. What I did or mine is..I had to drive back to college one day so I just drove with the radio off for 2.5 hours then I attempted the code again (follow the unlock steps above) and it unlocked fine (since I waited).
2. Now that you are sure that the car itself has been running well over 2 hours, move back up to the unlock steps and attempt at entering your unlock code again.
3. If you are still having trouble with this, you can resort to going to a BMW dealership and letting them enter the code for you. I'm pretty sure that they will enter the code free of charge at most dealerships.
Good luck with that, and stick around here!