missing degree of freedoms.

模型总是出现如下错误：2 nodes are missing degree of freedoms. The MPC/Equation/kinematic coupling constraints can not be formed. The nodes have been identified in node set ErrNodeMissingDofConstrDef.
底部的刚体和中间的物体是tie 粘结。上面的也是。
从错误信息可以看出，两个刚体的参考点出错。