C# MWMCR::EvaluateFunction error undefined function 'splinelev' for input arguments of type 'double'

I have created a .dll package in Matlab 2012a,the m file as follow：

function z = curveFitFunc(x,y,d)

xx = [min(x):d:max(x)];

opts = fitoptions('mtthod','smoothing');

ffunc = fittype('smoothingspline');

f = fit(x',y',ffunc,opts);

z = feval(f,xx)';

end

1.and open the deployment tool window: deploytool

2.build the .net component.

3.write source code for a C# application

I use visual studio 2010

4.build and run the application in visual studio .NET

the error is :

MWMCR::EvaluateFunction error

undefined function 'splinelev' for input arguments of type 'double'

the 'splinelev' is the MEX file in MATLAB at

'R2012a/toolbox/curvefit/curvefit/private/splinelev.mexw64'

I don't know how to solve the error, anyone can help me? thanks a lot!