The cause of this issue probably lies with the mesh interfaces. When mesh interfaces are located between periodic boundaries, Fluent sometimes builds additional periodic threads, losing linkage to their parent threads while being saved. This causes a segmentation violation when trying to run the simulation from the saved case. You can verify this error source for your case by deleting all interfaces from the saved (and reread) case. If unwanted boundary zones wall-xy and wall-shadow-xy still exist, you are experiencing the mentioned issue. To resolve the problem, you must prevent Fluent from creating the additional periodic threads by setting a Scheme variable from the TUI as follows: (rpsetvar ‘nonconformal/allow-interface-at-periodic-boundary 0) You must do this before creating the Mesh Interfaces. NOTE: You cannot heal an already “damaged” case by reading a BC-file and using the above rpsetvar command