This following Warning may appears in CFX-Solver from v18.1: ” Topology simplification is activated with the following restrictions: – Mesh regions referenced only within User Fortran and NOT in the command file will cause the solver to stop. – The solver will stop during any “Edit Run in Progress” step if new 2D regions are referenced. ” This warns that only the mesh regions defined in the Domains and Boundary Conditions in CFX-Pre will be saved in the .def file for the calculation. So no additional Region can be used in user Fortran or during Edit Run In Progress option during the calculation. So in the majority of the cases, this warning won’t affect the calculation.