this array elements must be scalar

Can not tell from the picture alone what the culprit may be.

Unless you expect a single value es result for the last expression (vector dot product) I guess that the expression needs vectorization.

For further help you should attach a worksheet. Preferably one with stripped down sample data not needing the Excel sheet which does show the same error.

Furthermore your program should return a value for ANY input (LoadCase) even though you may think that the case can not exist.
Your program so far does not provide a return value for LoadCase <100, LoadCase>408 and LoadCase in the range from 208 to 400! Guess this is the reason for the error.

You are on the safe side if you use "else if" and "else" and also explicit "return" statements (not mandatory, but good style).

You may omit the return statements

or you may omit the "else" branches

but not both (as otherwise the result would always be 0 or whatever you choose as return value for LoadCases not in the two ranges [100;208] or [400;408])

You may also use the if-function instead of the programmed if-statement

and you may even create the very same vector without using the range "r" is as follows:

Note that the expression has to be vectorized.