C++ window Dialog error

#include <windows.h>
#include "resource.h"
const char g_szClassName[] = "myWindowClass";


// defining dialog box
    IDD_ABOUT DIALOG DISCARDABLE  0, 0, 239, 66
    STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
    CAPTION "My About Box"
    FONT 8, "MS Sans Serif"
    BEGIN
        DEFPUSHBUTTON   "&OK",IDOK,174,18,50,14
        PUSHBUTTON      "&Cancel",IDCANCEL,174,35,50,14
        GROUPBOX        "About this program...",IDC_STATIC,7,7,225,52
        CTEXT           "An example program showing how to use Dialog Boxes\r\n\r\nby theForger",
                        IDC_STATIC,16,18,144,33
    END

// about us dialog procedure
BOOL CALLBACK AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
    switch(Message)
    {
        case WM_INITDIALOG:

        return TRUE;
        case WM_COMMAND:
            switch(LOWORD(wParam))
            {
                case IDOK:
                    EndDialog(hwnd, IDOK);
                break;
                case IDCANCEL:
                    EndDialog(hwnd, IDCANCEL);
                break;
            }
        break;
        default:
            return FALSE;
    }
    return TRUE;
}

// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_CREATE:
        {
            HMENU hMenu, hSubMenu;
            HICON hIcon, hIconSm;
            hMenu = CreateMenu();
            hSubMenu = CreatePopupMenu();
            AppendMenu(hSubMenu, MF_STRING, ID_FILE_EXIT, "E&xit");
            AppendMenu(hMenu, MF_STRING | MF_POPUP, (UINT)hSubMenu, "&File");
            hSubMenu = CreatePopupMenu();
            AppendMenu(hSubMenu, MF_STRING, ID_STUFF_GO, "&Go");
            AppendMenu(hMenu, MF_STRING | MF_POPUP, (UINT)hSubMenu, "&Stuff");
            hSubMenu = CreatePopupMenu();
            AppendMenu(hSubMenu, MF_STRING, ID_HELP_ABOUT, "&About");
            AppendMenu(hMenu, MF_STRING | MF_POPUP, (UINT)hSubMenu, "&Help");
            SetMenu(hwnd, hMenu);
        }
        break;
        case WM_COMMAND:
        switch(LOWORD(wParam))
        {
            case ID_HELP_ABOUT:
            {
                int ret = DialogBox(GetModuleHandle(NULL), 
                    MAKEINTRESOURCE(IDD_ABOUT), hwnd, AboutDlgProc);
                if(ret == IDOK){
                    MessageBox(hwnd, "Dialog exited with IDOK.", "Notice",
                        MB_OK | MB_ICONINFORMATION);
                }
                else if(ret == IDCANCEL){
                    MessageBox(hwnd, "Dialog exited with IDCANCEL.", "Notice",
                        MB_OK | MB_ICONINFORMATION);
                }
                else if(ret == -1){
                    MessageBox(hwnd, "Dialog failed!", "Error",
                        MB_OK | MB_ICONINFORMATION);
                }
            }
            break;
            case ID_FILE_EXIT:
                PostMessage(hwnd, WM_CLOSE, 0, 0);
            break;
            case ID_STUFF_GO:

            break;
        }
        break;
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;
        case WM_DESTROY:
            PostQuitMessage(0);
        break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    //Step 1: Registering the Window Class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

    if(!RegisterClassEx(&wc))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }


    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "The title of my window",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
        NULL, NULL, hInstance, NULL);

    if(hwnd == NULL)
    {
        MessageBox(NULL, "Window Creation Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // Step 3: The Message Loop
    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}