请问，求解时弹出这样的对话框是什么意思？

请问，求解时弹出这样的对话框是什么意思？
A small negative equation solver pivot term has been encountered at the UZ degree of freedom of node 149.Check for an insufficiently constrained model.
问题出在哪里啊？这样的问题怎么解决啊？求高人指点。