can you advise in regard to this simply supported beam analysis?
It seems boundary conditions have not been defined.
I followed the procedure described in your guidelines. I defined rigid links and elastic links to the support.
I attach the model for your better understanding.
The reason for this error is that the support boundary conditions are assigned to the nodes, however, the nodes are not activated in the stage. The structural group only includes the elements and nodes at the deck level, so the supports nodes are not activated.
All you need to do to get the model running is to include the support nodes (where the supports are and the ones connecting the links) in the structural group activated in the first stage.