Re: Central Locking Problems?!
If it beeps and arms the alarm but the door pins don't go down it could be because one of the doors is not properly shut - give them all a good slam!
When it's icey, my wife's GTV will sometimes disarm the alarm but only release the door pins for a second or too before re-locking (but not re-arming the alarm). If you can't get the door open in that 2 second window, try using the key in the lock. Note that it only ever does it when the temperature is below zero and not all the time when it is!
Other than the above, I can only suggest that one of the pins/sensors is not working properly which could confuse the system.
Hope this helps but if you find a different cure do let us know!