Thats BS. I would fight that tooth

and nail. If the manager is no use, contact the district manager. Let him know how you feel, and that you booked the room a month in advance, ruined a very special night. That should do it, im sure. If not, mention your calling the local tv station and file a complaint. Hotels HATE bad publicity.. who doesnt.
If they were reputable, they would of either put you up in another hotel on the house, or offered you a stay at a later date free of charge.
Do something about it.