I believe its because of the way you define the contacts. As you defined the rail as a "beam", when you define the contacts you got to choose the rail and use the beam option as such:
Do it for all the parts which bonds to the beam as such, and you will be able to run the study:
Hope this helps
thanks David, i think you are correct.
Btw, do you know how global contact works? With my defined contacts, does it necessary to suppress the global contact?
Thats a really good question, and honestly I have not gotten a solid answer on this myself.
From my experience using simulation this is what I can gather:
You dont have to suppress global contacts when you have contact sets, as SW Sim will resolve contact sets first, and then use Global contact everywhere else with no defined contact sets.
Global contact seems to work well when the mesh types are of the same kind, such as between solid-solid, shell-shell and beam-beam. However if you have mix meshing type, you then must use contact sets.
You might want to verify these points first for safety.