i got error as number of parametr should be greater than number of data.help me

Help me for this

when i try to use the follow s-function in a simulink blocket, i obtain this error

Error in 'estimatorTUDRLS/S-Function3' while executing M-File S-function 'estimatorTudrls', flag = 2 (update), at time 0. MATLAB error message:
Number of data should be greater than the number of parameters!

function [sys,x0]=estimatorTudrls(t,x,u,flag,ts,para_ini,na,nb,d,Fin,lam1,lam0)
if flag==0
sys=[0,4,4,9,0,2];
% 0 continuous states; 4 discrete states; 2 outpus;  9inputs;
% 0 discretes roots; 0 direct feedthrough;
x0=para_ini; % 6*1 row vector;
elseif flag==1
sys=[];
elseif flag==2
u1=u(1); y=u(2);
[B,A]=udrlsT(y,u1,na,nb,d,Fin,lam1,lam0);
x(1)=B;
x(2)=A;
x(3)=C;
x(4)=D;
sys=x';
elseif flag==3
sys=x(1:4);

elseif flag==4
    sys=[];

else sys=[];
end