MATLAB Builder Ex does not run Fuzzy Toolbox functions in Excel

Hi,

I have a very simple function ...

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function x = y(a,b,c)

z = readfis('fuzzy_model');

x = evalfis([a b c],z);

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It compiles fine into an Excel Add-In, however when I run it in Excel, I get all sorts of erros like:-

-- Undefined function 'readfis' for input argument of type 'char'.

I then saved the fuzzy structure into a .mat file to avoid this error, however it then breaks on the next line in Excel:-

-- Undefined function 'evalfis' for input argument of type 'struct'.

Does the builder not compile the fuzzy toolbox functions??

Thx