The Physics Solver Properties pane lets you specify basic constraints or default conventions that govern the solving behavior. 
Note: On 64-bit systems, the Physics Solver cannot process objects that have degenerated polygons or invalid normals. When this occurs, a warning message appears that identifies the models that have this problematic geometry, and bounding boxes are used to approximate these shapes instead. Using these bounding boxes for the joint solve may produce solve results that differ from the expected behavior. If possible, use the Box, Capsule, Sphere, or Mesh approximations to match your geometry with more precision. For more complex geometry, reconstruct your model with 3D software to avoid these non-standard geometry problems. This problem does not occur in the 32-bit version of MotionBuilder.