Answer:
The message about the incorrect addition of load cases should be considered as an indication: It appears as soon as load cases of a nonlinear system (for example, with tension members) are superimposed in an RC.
Eventually, there can be a different structural system for each load case, since different members are effective. In DYNAM Pro, your structural system is linearized when using the response spectrum analysis. Therefore, this message is always displayed when nonlinear elements exist in the model.
