My bmw 320d remote wont lock car however does lock the car with the key its a 55 reg

1
Programming
When
Key batteries completely discharged. Key batteries not replaced within 60 seconds. Key added or replaced. DO NOT press remote control buttons during battery replacement.
How
Unlock vehicle. Enter vehicle. Close driver's door. Switch ignition ON and OFF. Remove ignition key. Press and hold unlock button Fig. 1 [1]. Press lock button Fig. 1 [2] briefly 3 times within 10 seconds keeping unlock button [1] depressed. Release unlock button Fig. 1 [1]. Some models: LED Fig. 1 [3] flashes slowly for 10 seconds. Some models: Central locking system locks and unlocks rapidly to indicate correct programming. Some models: Repeat above procedure if central locking system does not work and LED does not flash or LED flashes continuously
Later keys with bmw badge on key. Battery can not be replaced
Battery in key charges while driving

Here's the link and I'm sure you will get the solution of your problem
Best Manuals