Hi mark, it may be possiable that the vaux com software is faulty.
I had a problem coding two keys to a vauxhall and said it was coded tryed to start car it would fire up and cut out. so i used AD
and it did the keys instantley. i then went to a second car astra 03
and tryed to sync two key fobs the same as you and vaux com would not do it. this only happend when i downloaded the latest.
vaux com. i had to use autodiagnos again to sync the key fobs.
HTH Greg