S-Function file for Inverted Pendulum system

S-function simulink error: during flag=1 call must be a real vector of length 4.

While trying to run the file in simulink it is showing that-
State derivatives returned by S-function during flag=1 call must be a real vector of length 4.
whereas I have maintained length 4 in the flag=1 as well as I have used real algebraic equations. No, question of complex vector coming. Why this error?? Plzz Help.