hello guys: please help me to design a model predictive controller for DC-DC converter

 I am trying to build a model predictive controller for a buck-boost DC-DC converter and I am using a embedded matlab bluk to included the converter's equation but every time I start designing the MPC model it gives me erred as in pic below
I included the code script and the full model design.
please help me 
thank you
Moh

[Ameer Hamza]

It seems that your model expects a column vector xpoff in the base workspace. Make sure that a variable with this name exists.