Okay thank you, i will try that. i am using revolute joints connected to the inside cylindrical surfaces of the bolt holes... am i using these right?

Edit: I have just tried what you suggested, and I am still receiving the same error.  I also replaced the revolute joints with general joints free only in rotation along the z-axis. i also changed the main support of the trailing arm from cylindrical as i realised it needs to be able to move slightly in all directions.