OK, my hypothesis here is that you created your script file using the GUI. My understanding is that when has a popup window that opens, the order that the relevant selection entities (i.e. faces or cells) will be ordered by the ID. Since the ID numbers have changed between the two meshes, the order and possibly the number of these, the GUI will have difficulty reconstructing exactly what you are trying to do.

So what are the solutions? One would be to go into Fluent meshing and rename and renumber the ids exactly how they were in the original script. I am not sure if this can be done in the GUI (if Rob is “listening” in maybe he can let us know). But I know it can be done using scheme. Unfortuantly my memory is not good enough to give you the exact command right now. But this would require a lot of bookkeeping if you have a large number of faces, which it seems you have.

The other approach would be to re-create your script using the TUI commands. Without looking at your script, I would imagine that all the commands using the TUI would let you used any named selections that you have created. This would be much more robust and allow you to import a third, fourth, fifth grid without trouble (if they have the same named selections). Plus, you would get the added benefit of learning the TUI which is a skill too many new users lack.

There is also the new Python approach that I am still trying to learn myself. And depending on what you are trying to accomplish, not all commands are fully integrated into Python. But in those cases where it is not, you could execute those commands using TUI commands (again, that is my understanding).