Have they got contracts or have they run out and a new one not issued or a new one not negotiated. I am afraid that you cannot force people to pay,do the people not pay because it is over priced maintenance are they unhappy with the complex and the way its run you could ask a lot of people and get different answers from them all its a chicken and egg question we have the same problem with a multitude of reasons so I do not think there is a answer to your question good luck anyway and if a way is found to get all the owners to pay let me in on it and I will make you famous.