Hi I have defined a generic c++ class in a .net project c++

In the definition (the header file) i declare a define a variable for
it

#pragma once

#include "categories.h"

#using <mscorlib.dll>
using namespace System;
using namespace System::Collections;

__gc class BooksOfEntry
{
public:
    String* BookName;
    Categories* categories1;
    ArrayList* CustomerOrders;

    BooksOfEntry(String* name);
    ~BooksOfEntry(void);
};

I am getting  problem compiling this ArrayList definition is causin
compiler errors.