There can be many reasons for the break down in the relationship. One of the main reasons is having a different vision over an aspect of the film -- use of funds, edit of the picture, certain hires, music and actor choices, etc.
Every relationship can and does have conflict. Problems arise when people don't work together. It takes a team to make a movie and when someone steps away from the team and tries to impose his or her viewpoint as the best and only means of addressing an aspect of or even the entire film then a crack in the bond of the creators is inevitable.
The worst part about having a fissure in the producing partnership is that it detracts from the main goal to which all energy should be focused: the successful creation of a motion picture. Infighting breeds stress and many wasted hours of discussion. Imagine if that energy could be used to help support the project instead of working against it? Imagine if the partners had worked together toward a compromise or common goal that both parties could believe in and feel comfortable with?
You may be saying, but I have tried to find that common goal. And perhaps you have. Solutions can only be made if both parties are committed to listen to one another and accept each other's opinion and find a solution that works for both parties. You can't make it happen by yourself. A filmmaking team is not made of one person's actions or decisions. If you have truly tried to repair the crack and your partner ignores your attempts and still wants to make it all about his or her ideas then all you can do is keep working hard toward making the best movie possible.
Some people don't have the strength to say, I need to put the film first. When a crack appears, everyone needs to step back and evaluate all factors of the picture. Does your or your partner's viewpoint make sense in the overall scheme of things? Are you really suggesting solutions that make sense for the film and the team and resources behind it and the film industry on the whole? Do you really understand how the industry works? Or could you be so focused on believing that you have the solution for what ails the project that you have forgotten that it takes a village to raise a child?
Let's not forget how hard it is to get a movie made. I know firsthand the many challenges and obstacles that need to be overcome. I have the scars from being knocked down, dragged through the mud, slammed into walls, and pulled through raging waters. I am humbled by what can go wrong and extremely proud of being able to make it over, under and through all the problems. Is it easy? Absolutely not. But is it necessary? Yes. You are a filmmaker and there will always be obstacles. Survival includes figuring out how to handle those obstacles and still make a great film.
So what do you do when you realize you have the wrong producing partner? All you can do is re-channel any energy spent on the crack in the relationship back into the successful creation and launch of your film. For the sake of the movie that you have spent years building, you need to set aside the stress of the partnership and figure out how to make the best product possible. Because in the end, the winner and loser of your partnership is your film.
Unfortunately, some people allow their ego or pride or lack of knowledge of the industry get in the way of putting the film first. They latch on to the idea that their way is the best and only way of completing the film and they terrorize those who do not fall in line with their vision. When this happens, all you can do is work hard to make the best movie you can make with the resources you have.
Look at all of the great leaders throughout history. You better believe they experienced conflict throughout their careers. No one is immune to conflict. It's how you react in moments of conflict that make you great. And in my opinion, the only way to react when you have the wrong producing partner is to focus on making the best film possible. For in the end, it's all about the movie, not you or your partner.