smException.sm (5.92 KiB) downloaded 25 time(s).smath-exception.doc (31.5 KiB) downloaded 18 time(s).
I get an exception while typing in a variable name into the worksheet, --after-- a recalculate. Not before. Anyone any idea what might be happening? The exception looks to depend on what's in the function call - for example, it's fine if N is set to 25, and fine on different variants of the function algebra. It's nothing to do with the variable name itself, it's not a reserved name conflict. It's repeatable and does it in Windows 10 and Windows 7. Sm and exception report included.

I can confirm the issue (and as you say, it works just fine with N=25).

From the error stack seems related to the handling of ChildrenRegions, even though the document seems has none of those.

Thank you Davide. Further probing shows it might be related to optimization : if I turn the vector generating loop optimisation away from symbolic to either numeric or none, the exceptions stop. Although the optimised and non-optimised variants do look to be very similar, so that might be spurious. This all originated in a larger document, with two same sized arrays generated by two similar function calls : one generated an exception when typing the vector name, the other didn't. N was originally 32, there are lots of values of N that don't cause an exception.