Model Predictive Control - State Space model - error message

In the model predictive control tool box of MATLAB R 2013a, i entered a discrete state space model with

A1=[0,0,0;0,0,0;0,0,1];
>> A2=[0,0,0,0,0;0,0,0,0,0;0,0,0,0,0;0,0,0,0,0;0,0,0,0,1];
>> A3=[0,0,0,0;0,0,0,0;0,0,0,0;0,0,0,1];
>> A=blkdiag(A1,A2,A3);
 B=[0,0,0;0,0,0;1,0,0;0,0,0;0,0,0;0,0,0;0,0,0;0,1,0;0,0,0;0,0,0;0,0,0;0,0,1];
C1=[0,0,1;0,0,0;0,0,0];
>> C2=[0,0,0,0,0;0,0,0,0,1;0,0,0,0,0];
>> C3=[0,0,0,0;0,0,0,0;0,0,0,1];
>> C=[C1,C2,C3];
 D=[0,0,0;0,0,0;0,-1,-1];
>> sys = ss(A,B,C,D,0.1);
0<=yi(t)<=2000; i=1,2,3
0<=ui(t)<=300;i=1,2,3
yi*=1000;i=1,2,3;

I am getting the error message " At least one manipulated variable has direct feedthrough in the MPC1 model. MPC calculation is aborted". where did i made the mistake.