Included header file is not being seen
===

I have a project with a few classes. Linking 2 of them together is giving me problems. These are the errors I get in Form1.h:

     (Form1) error C2871: 'OpenGLForm' : a namespace with this name does not exist
     error C2653: 'OpenGLForm' : is not a class or namespace name
     error C2143: syntax error : missing ';' before '^'
     error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
     error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
     error C2065: 'OpenGL' : undeclared identifier
     ... they're all because of missing header, I'm pretty sure

This is the top of Form1:

    #include "OpenGL.h"
    
    #pragma once
    
    namespace GUI_1 {
    
    	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 OpenGLForm;
    	using namespace std;
    	using namespace System::Runtime::InteropServices;

This is OpenGL.h:

    #pragma once
    #pragma comment(lib, "opengl32.lib")
    #pragma comment(lib, "glu32.lib")
    
    #include <windows.h>
    #include <GL/gl.h>
    #include <GL/glu.h>
    #include <GL/glut.h>
    #include <math.h>
    #include "Form1.h"
    
    //.... some global variables ... 
    
    using namespace System::Windows::Forms;
    
    namespace OpenGLForm 
    {
    	public ref class COpenGL: public System::Windows::Forms::NativeWindow
    	{
    	public:
    		....
    	private:
    		....
    
    	protected:
    		....
    	};
    }

And OpenGL.cpp:

    #include "stdafx.h"
    #include "OpenGL.h"
    #include <windows.h>
    
    using namespace System::Windows::Forms;
    ...


I have searched online, but only found this problem related to System namespaces, nothing for your own. The linking between the two headers worked fine before I split OpenGL into .cpp and .h (before I just had .h).

Thanks in advance!

