using c++ MFC dll in c# code - SEHExceptio

Question

Hi,

I am a computer science student and I am developing a web-application in C# for a company as my master thesis. The web-application I am developing is an additional tool for an existent desktop application written in C++.
One of the requirements I have to accomplish is to keep the same layout interface in a web page as a window in the desktop application. This window contains a grid where there are some objects that the customers can drag and drop. The desktop application loads this grid at the window start-up and saves the grid every time it is modified (and the window shuts down). The grid is saved in a binary format by using serialization.
So I need to create a MFC dll as middle layer between my web application and the classes of desktop application that saves and load the grid. The grid’s objects are saved in a CMapToStringOb object, and this object is inside another class that is the one saved on the binary file. To better understand:

class CObjectLayout : public CObject { 
   DECLARE_SERIAL(CObjectLayout) 
   //.. constructor decostructor
public: 
   virtual void Serialize(CArchive& ar);
private: 
   CMapStringToOb* objectView;
   // .. other data
}

An instance of this class is saved in the binary file. In fact, in the window class contains the following Serialize method

void CWindow::Serialize(CArchive& ar) { 
   if (ar.IsStoring()) { 
      //objectLayout is defined as CObjectLayout*
      ar.WriteObject(objectLayout);
} 
   else { 
      if( m objectLayout != NULL ) 
         delete m objectLayout; 
      objectLayout = (CObjectLayout *) ar.ReadObject(RUNTIME_CLASS(CObjectLayout)); 
   }
}
I created my MFC Dll called CMiddleLayer as
class CMiddleLayer {
public:
CMiddleLayer();
~CMiddleLayer();
private:
CObjectLayout* objectLayout;
public:
virtual void Serialize(CArchive &ar);
LPCTSTR returnXPosition(LPCTSTR objectName);
// .. and other similar methods
};

The Serialize method is exactly the same as the one in CWindow class and it is called inside the method returnXPosition (it is not a good thing load all everytime, but it is just to try if it works).
I also added the following functions to export the class methods:

extern "C" __declspec(dllexport) CMiddleLayer* MiddleLayer_Create(){return new CMiddleLayer();}
extern "C" __declspec(dllexport) LPCTSTR MiddleLayer_Return(CMiddleLayer* MiddleLayer, LPCTSTR objectName){return MiddleLayer-> returnXPosition (objectName);}
extern "C" __declspec(dllexport) void MiddleLayer_Delete(CMiddleLayer* MiddleLayer){delete MiddleLayer;}

In c# code I imported the dll in the following way:

[DllImport(@"myDllMFC.dll")]
private static extern IntPtr MiddleLayer_Create();
[DllImport(@"myDllMFC.dll")]
private static extern string MiddleLayer_Return(IntPtr value, string objectName);
[DllImport(@"myDllMFC.dll")]
private static extern void MiddleLayer_Delete(IntPtr value);

I created a label wherein loads the XPosition:

IntPtr pointer = MiddleLayer_Create();
Label.Text = MiddleLayer_Return(pointer, “objectName”);

When I try to run the web application, it gives back a SEHException at the Label.Text=.. line.
I found out that the MFC dll crashes at the line wherein the CObjectLayout object is loaded from the file (objectLayout=(CObjectLayout *)..).
I tried everything I found around the web but I don’t understand how to solve it. If it can help, I tried to take out just a byte from the file and it works.

Can anyone help me?
Do you think there is a way to solve it by carrying on using this way to save and load the data?
At least tell me if there is no way to solve it and I will try to save the object data in a different way, even if it will take more time.

Thans a lot
Davide

P.S. I am italian.. so sorry for my english..