Ziggie

My passat has trouble opening the central locking. The garage replaced key 12 months ago. The key has now intermittently stopped unlocking ( locks ok) but I can unlock it using the other key. a garage reported that the alternate key had failed yo unlock for him . he used the backup method of opening the door. The new key cost £400 + service charge to register it to the car. Is this a common problem? any DIY method of fixing?