C++ dll plugin problem.

I just made C++ dll. when i read the dll in Unity, Unity crash down. Folloing is the steps.

tool: vs2008

step 1) vs2008 => new => Project ==> Visual C++ ==> CLR ==> Class Library projectname is clrtest.

step 2) clrtest.h

#pragma once 
#using <mscorlib.dll> 

using namespace System; 

namespace clrtest { 

    public ref class Class1 
        int Add(int a, int b) { return a + b; }; 

step 3) compile ==> copy clrtest.dll into unity plugin folder.

step 4) in unity c# script

using UnityEngine; 
using System; 
using System.Collections; 
using System.Collections.Generic; 
using System.Runtime.InteropServices; 

using clrtest; 

public class mycowcontrol : MonoBehaviour {  

    void Start() 
        clrtest.Class1 temp = new clrtest.Class1(); 
        int x = temp.Add(1, 2); 
        Debug.Log("1+2 = " + x); 


step 5) execute and just down.

I don't know why the unity is down. is any problem my c++ dll making procedure?

please let me know if you have any idea. Any help would be much appreciated.

See the answer to Considerations/Gotchas when Creating a C++ CLR Plugin in VS2008.