I am trying to do vehicle control. I am trying to use the magic formula which is given by

@defNLExpr(mdl, FyR[i = 1:N] , D*sin(C*atan(B * (atan((v_y[i] - b*r[i])/v_x[i])))) )

Now when i run the code i am getting a error:

EXIT: Invalid number in NLP function or derivative detected.

WARNING: Ipopt finished with status Invalid_Number_Detected

How do I get around this problem?