Sizes vector returned by MATLAB S-function

After I compile this S-function:

   function [sys,x0,str,ts] = Derivative1(t,x,u,flag)
    global n;
    switch flag,
          case 0,
        [sys,x0,str,ts]=mdlInitializeSizes(n);
         case 3,
        sys=mdlOutputs(t,x,u,n);
        case {1,2,4,9}
            sys=[];
        otherwise
            error (['Unhandled flag= ',num2str(flag)]);
    end
    function [sys,x0,str,ts] =mdlInitializeSizes(n)
    global sample_time
    sizes=simsizes;
    sizes.NumContStates  = 0;  
    sizes.NumDiscStates  = 0;  
    sizes.NumOutputs     = n;  
    sizes.NumInputs     = -1;  
    sizes.DirFeedthrough = 1;  

    sizes.NumSampleTimes = 1; 

    sys = simsizes(sizes);

    x0  = [];               

    str = [];                 

            ts= [sample_time 0];
        function sys=mdlOutputs(t,x,u,n)
            global sample_time
            z=0;
            for i=1:(n-1)
                if (t>=sample_time*i)
                    z(i)=((-1)^i)*diff(u([1:[i+1],i]),i)/(sample_time^i);
                else z(i)=0;
                end
            end
                sys=[u(1),z];

                return

The compiler generates an error: Sizes vector returned by MATLAB S-function 'Derivative1' in 'Adaptive_Controller/Adaptive Controller /Derivative1' must be a real vector consisting of integer value of length 7 Please tell me what I do wrong. Thank you in advance.