二维桁架分析出现的错误日志

在进行二维桁架分析时，ERROR提示 Nodes I and J of element 8 ( LINK1) use the same node number. 顺便图上附上所有单元信息，而且在我施加完约束和力后，系统提示The value of UY at node 1 is 3.157605501E+13. It is greater than the
current limit of 1000000. This generally indicates rigid body motion
as a result of an unconstrained model. Verify that your model is
properly constrained. ，可我施加的力只有250LB，难道是英制不需要单位转换？此题中桁架长度均为ft,实在搞不懂求解答。