The central locking (open) motor on the driver's door may be faulty or a wire is broken connecting to the motor. The ECU is probably trying to unlock the door when you press the button, but failing. Once you have unlocked the drivers door manually, the ECU is then able to unlock the others.
Do you have a button inside the car that can lock and unlock the doors? If you do, see if you can lock then unlock the driver's door from inside, if you can't unlock it from inside, this would back up my thought about the motor being faulty.
Do the lights usually flash when you press the button? If they still flash when you try to unlock the drivers door, then this would back up that the communications between the remote and the ECU are fine, and you have a problem with the motor in the driver's door central locking.