747-200B Cant fly R2

Have you checked the runway requirements for the 747-200B? If I recall correctly the runway required is longer than that available at DUB so this will be why your aircraft can't be added to that route.

Dublin's longest runway is about 8,500 feet, but the 747=200B requires a minimum of about 9,100 feet. That is probably the reason why you can not use the -200B on that route.