During back substitution 2503 elements encounter a load applied to a degree of freedom that does not have any stiffness. The elements have been identified in element set WarnElemBackSubNoStiffStep1Inc1.

• 这个错误是什么意思?如何解决?字面上看一个荷载加到一个没有刚度的节点上怎么解释?谢谢！