Error while using Matlab COM

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C#

COM

MatLab

Rencently I compiled C# program to call the matlab COM called NLregression1 which compiled by myself to solve the problem of nolinear regression of data.I used the matlab function as follow:nlinfit,nlpredci and exponen which is used in the nlinfit, when the program to run ,there always is errors:nlinfit at 120 ; error evaluating model function'exponen'; error in =>NLregressionP1.m at 25.
But I run the matlab program NLregression only ,it run well in matlab. the code as below:
c#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using NLregression1;

namespace nlreg2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double[] y = { -0.5, -0.1, -0.2, 0, 0.1, 0.4, 1, 0.2, 0.1 };
            int[] x = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
            int[] beta0 = { 2, 8 };
           NLregression1Class nl = new NLregression1Class ();
            object obj_x = (object)x;
            object obj_y = (object)y;
            object obj_beta0 = (object)beta0;
            try
            {
                nl.NLregression(obj_x, obj_y, obj_beta0);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}

matlab:

function NLregression(x,y,beta0)
[beta,r ,J]=nlinfit(x,y,@exponen,beta0);
[YY,delta]=nlpredci(@exponen,x,beta,r ,J);
plot(x,y,'k+',x,YY,'r')
end

 function yhat=exponen(beta,x)
      yhat=beta(1)*exp(beta(2)./x);
 end

so is there some kind person who can help me ?