Using 1.12.2.120, I created this geometry in a new model:

(note: The above screen showing the geometry does not necessarily correspond to the state of FEATool when the following errors appeared)
Upon attempting to save it as a model file I got this error:

I then saved it as a script:
cylinders_between_cylinders.fesThen started a new model and loaded the saved script. When the script finished executing, I got this similar but different error:

What might be the problem? What else should I provide to help?
-Randal
Edit: Just installed 1.12.2.121 and encountered same behavior on saving as model.