Dear @raksha,
The termination error is due to the fact Fluka tries to expand the parenthesis runtime but fails. This regardless of the correctness of the geometry definition, i.e. there might not be error in the definition, but the runtime expansions of the parenthesis gets too many terms and Fluka cannot handle it.
You can try to expand the parenthesis in Flair before running, in the “Geometry” tab, in the “Region” section of the ribbon, with the option “Expand”, I’m not sure what you are referring too with the option “Correct”.
Unfortunately for you, Flair fails the expansion. I cannot tell you why, but your SHIELD2 region seems quite complicated.
I suggest you to rewrite by hand its definition removing the parenthesis or at least as many as you can. Then you might even try again with the “Expand” option.
Good luck