How can I deal with a 3rd party by grud affecting business?

I provide equipment to caterers for their events. 5 years ago, there was an event at a hall that my company (not owned by me yet) provided service to the caterer for the event. The driver at the time left a bad impression on the person in charge of the hall. Since I purchased this business, I have to say, the service has increased dramatically and sales have been impressive. We have serviced caterers to their satisfaction and I have now heard from 3 different caterers that the hall manager is discouraging the renter form using our service, but it is the high-class caterer that is requesting our service, not the hall manager. We still have been able to provide the service and no screw-ups. The hall manager is still telling bad tells. How would you handle this? Consider that if I go over that persons head, which has been there for many years, they will most likely try to hurt our business even more. Talking to the hall manager has gotten NO WHERE. Any impressive Suggestions?How can I deal with a 3rd party by grud affecting business?
I would take the Hall Manager out to lunch and very nicely ask him how you can work TOGETHER to get more business.