Dynamic DLL Help

///////////////////////
//In main.cpp
///////////////////////
LoadDevice()
{
	Log->LogInfo("Creating device...");
	switch(driver)
	{
	case DT_DIRECTX9:
		hDLL = LoadLibrary ("D3DDriver.dll");
		if (!hDLL)
		{
			MessageBox(NULL, "Loading D3DDriver.dll failed.", "Lion Engine  - error", 
				       MB_OK | MB_ICONERROR);
			return NULL;
		}
		Log->LogInfo("\tLoaded D3D DLL");
		break;
	case DT_OPENGL:
		hDLL = LoadLibrary ("OpenGLDriver.dll");
		if (!hDLL)
		{
			MessageBox(NULL, "Loading OpenGLDriver.dll failed.", "Lion Engine  - error", 
				       MB_OK | MB_ICONERROR);
			return NULL;
		}
		Log->LogInfo("\tLoaded OpenGL DLL");
		break;


	default:
		MessageBox(NULL, "API Unsupported", "Lion Engine - error", MB_OK | MB_ICONERROR);
	}

	CREATERENDERDEVICE _CreateRenderDevice = NULL;

	// pointer to DLL function ‘CreateRenderDevice’
	/*_CreateRenderDevice = (CREATERENDERDEVICE)

	GetProcAddress(hDLL, "CreateRenderDevice");*/

	_CreateRenderDevice = (CREATERENDERDEVICE)::GetProcAddress(hDLL, "CreateRenderDevice");
	if (!_CreateRenderDevice )
	{
//////////////////////
		//I get this error message
///////////////////////
		Log->LogError("\tAddress is NULL");
		return NULL;
	}

	Log->LogInfo("\tFound address of function 'CreateRenderDevice'");

	// call DLL function to create the device
	if(false == _CreateRenderDevice(hwnd, hDLL, &RenderDevice))
	{
		Log->LogError("\tFailed to create device");
		MessageBox(NULL, "CreateRenderDevice() from lib failed.", "Lion Engine - error", 
			       MB_OK | MB_ICONERROR);

		RenderDevice = NULL;
		return NULL;

	}
	Log->LogInfo("Device created");
	return RenderDevice;
}

///////////////////////////////////////////////
//In a included header file...(IRenderDevice.h)
///////////////////////////////////////////////
#include <windows.h>
//Helper functions to create device from DLL
extern "C"
{
bool CreateRenderDevice(HWND hwnd, HINSTANCE hDLL, IRenderDevice **pInterface);
typedef bool (*CREATERENDERDEVICE) (HWND hwnd, HINSTANCE hDLL, IRenderDevice **pInterface);

bool ReleaseRenderDevice(IRenderDevice **pInterface);
typedef bool(*RELEASERENDERDEVICE) (IRenderDevice **pInterface);
}

#endif //Include guard

/////////////////////////////////////////////////
//In the DLL definitions...(CD3DRenderDevice.cpp)
/////////////////////////////////////////////////
//Defined in IRenderDevice.h
bool CreateRenderDevice( HWND hwnd, HINSTANCE hDLL, IRenderDevice **pDevice )
{
	if (!*pDevice )
	{
		*pDevice = new CD3DRenderDevice(hwnd, hDLL );
		return true;
	}

	return false;
}
bool ReleaseRenderDevice(IRenderDevice **pDevice )
{
	if ( !*pDevice )
	{
		return false;
	}

	delete *pDevice;
	*pDevice = NULL;

	return true;
}