小弟我用InsertMenuItem插入的菜单为什么是灰的

我用InsertMenuItem插入的菜单为什么是灰的?
在CMainFrame里有如下代码:
WIN32_FIND_DATA   bDileData;
HMENU   m_Menu   =   ::GetMenu(m_hWnd);
HMENU   m_PopupMenu   =   ::GetSubMenu(m_Menu,3);

MENUITEMINFO   m_Mii;  
m_Mii.cbSize   =   sizeof(MENUITEMINFO);
m_Mii.fMask   =   MIIM_TYPE   |   MIIM_ID;
m_Mii.fType   =   MFT_STRING;
m_Mii.dwTypeData   =   TEXT( "TEST_____ME ");
m_Mii.wID   =   WM_USER+USER_MENU+1;//USER_MENU在前面已经定义;
::InsertMenuItem(m_PopupMenu,ID_NULL,false,&m_Mii);
return;
可是菜单显示却是灰的,用EnableMenuItem改变也改不了,EnableMenuItem返回0值;
高手们给看看!


------解决方案--------------------
CMainFrame::CMainFrame()
{
// TODO: add member initialization code here
m_bAutoMenuEnable = FALSE; //加上这句就可以了，具体可看MSDN！
}