S_Function - Process modeling help

Hi,

I am trying simulate a process (MSF Desalination) using s_function in simulink. Since I am new to simulink, I have the following doubts.

The system I have has 108 states and 234 outputs and inputs each. The states are discrete and I am using my own derivative calculation functions to calculate the state values at the next time step. The outputs that I calculate at each time instant is to be used in the next time instant for calculation.

a) When I try running the model, I get the error message saying: "Output returned by S-function xxxxx during flag=3 call must be a real vector of length 234". What should be done to correct this?

b) The s_function code I have written is given:

Any help really appreciated. Thanks for your time.

    function [sys,x0,str,ts] = MSF_sfcn(t,x,u,flag)

    switch flag

    % Initialization
    case 0

        clc

        [sys,x0,str,ts] = mdlInitializeSizes;

    % Calculation of derivatives    
%     case 1
%         
%         sys = dynamic_MSF(x);
%          
    case 2

        % Write here the code to call a function which will calculate the
        % derivatives at that time instant. This should return just the
        % states

         sys = mdlUpdate(t,x,u);
%         
%         sys

    % Output    
    case 3

        % Write here the code to call a function that will update the
        % values of all the flow rates and other variables. These
        % recalculated variables will be the output. 

        sys = mdlOutputs(t,x,u);

    case {1 4 9} % Unused flags

        sys = [];

    otherwise

        error(['Unhandled fag =',num2str(flag)]);

end