桁架单元与实体单元MPC约束

   各位大佬好，我建了一个模型，拉索牵引水管的模型，拉索建立的桁架单元，水管建立的实体单元，两者通过MPC的PIN约束，控制点选取桁架单元端点，从节点选择水管的一端上端面。提交作业时，报错显示桁架单元已经被其他方程消除了  MPC，刚体，运动耦合约束。

   所以我想请教一下大神们，那我要在实体和桁架单元间 施加pPIN约束要怎么做？？？

DAT文件报错如下：

***ERROR: DEGREE OF FREEDOM 2 DOES NOT EXIST FOR NODE 7720 INSTANCE 

           LASUOFENXI-1-1. IT HAS ALREADY BEEN ELIMINATED BY ANOTHER EQUATION, 

           MPC, RIGID BODY, KINEMATIC COUPLING CONSTRAINT, TIE CONSTRAINT OR 

           EMBEDDED ELEMENT CONSTRAINT. THE REQUIRED MPC (TYPE PIN) CANNOT BE 

           FORMED.

 ***ERROR: DEGREE OF FREEDOM 3 DOES NOT EXIST FOR NODE 7720 INSTANCE 

           LASUOFENXI-1-1. IT HAS ALREADY BEEN ELIMINATED BY ANOTHER EQUATION, 

           MPC, RIGID BODY, KINEMATIC COUPLING CONSTRAINT, TIE CONSTRAINT OR 

           EMBEDDED ELEMENT CONSTRAINT. THE REQUIRED MPC (TYPE PIN) CANNOT BE 

           FORMED.

 ***ERROR: DEGREE OF FREEDOM 1 DOES NOT EXIST FOR NODE 7721 INSTANCE 

           LASUOFENXI-1-1. IT HAS ALREADY BEEN ELIMINATED BY ANOTHER EQUATION, 

           MPC, RIGID BODY, KINEMATIC COUPLING CONSTRAINT, TIE CONSTRAINT OR 

           EMBEDDED ELEMENT CONSTRAINT. THE REQUIRED MPC (TYPE PIN) CANNOT BE 

           FORMED.

 ***ERROR: DEGREE OF FREEDOM 2 DOES NOT EXIST FOR NODE 7721 INSTANCE 

           LASUOFENXI-1-1. IT HAS ALREADY BEEN ELIMINATED BY ANOTHER EQUATION, 

           MPC, RIGID BODY, KINEMATIC COUPLING CONSTRAINT, TIE CONSTRAINT OR 

           EMBEDDED ELEMENT CONSTRAINT. THE REQUIRED MPC (TYPE PIN) CANNOT BE 

           FORMED.

 ***ERROR: DEGREE OF FREEDOM 3 DOES NOT EXIST FOR NODE 7721 INSTANCE 

           LASUOFENXI-1-1. IT HAS ALREADY BEEN ELIMINATED BY ANOTHER EQUATION, 

           MPC, RIGID BODY, KINEMATIC COUPLING CONSTRAINT, TIE CONSTRAINT OR 

           EMBEDDED ELEMENT CONSTRAINT. THE REQUIRED MPC (TYPE PIN) CANNOT BE 

           FORMED.