#pragma once
#include "stdafx.h"
#include "form1.h"

namespace CursorEx{
    public ref class RenderCur
    {
    public:
        RenderCur();
        ~RenderCur();
    }
    private:
        Bitmap^ cursorImage;
}

#include "stdafx.h"
#include "cursorEx.h"
using namespace CursorEx;
RenderCur::RenderCur()
{
}
RenderCur::~RenderCur()
{
}

public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            CursorEx::RenderCur ^ c1;
            CursorEx::RenderCur ^ c2 = gcnew CursorEx::RenderCursor;

        }
...

#pragma once
#include "cursorEx.h"
namespace MyProgam{

    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;
    using namespace System::Threading;

    using namespace CursorEx;//Ошибка C2871

    /// <summary/>
    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            CursorEx::RenderCur ^ c;

namespace CursorEx{
ref class MyProgram::Form1; // Forward declaration

    public ref class RenderCur
    {
    public:
        RenderCur(MyProgram::Form1^ form);
        ~RenderCur();
    }
    private:
        Bitmap^ cursorImage;
}