Dear Richard,
I think you are right is about the rigid element. Yes, i have Rigid element in this model. but can the output be so different like that, it is almost 100 % different in mode shape result, but strange the other result is 85% the same. I try to attach my model, but it my office is close due to Christmas. If i get the model, i will send it to you. but meanwhile can you suggest me anything to do with the input?