C#下安装钩子函数在Win7下 总是返回,0，即失败，是什么原因？

Question

同样的代码，在XP下运行和win7下运行，XP下能安装钩子成功，但是win7下就返回失败。
是什么原因？ 代码如下：public bool InstallHook()
        {           IntPtr pInstance = (IntPtr)4194304;
            if (this.m_pKeyboardHook == IntPtr.Zero)
            {
                this.m_KeyboardHookProcedure = new HookProc(KeyboardHookProc);
                this.m_pKeyboardHook = SetWindowsHookEx(idHook, m_KeyboardHookProcedure, pInstance, 0);               
                if (this.m_pKeyboardHook == IntPtr.Zero)
                {
                    this.UnInstallHook();
                    return false;
                }
            }            return true;
        }        private int KeyboardHookProc(int nCode, Int32 wParam, IntPtr lParam)
        {
            //return 1;
            KeyMSG m = (KeyMSG)Marshal.PtrToStructure(lParam, typeof(KeyMSG));
            if (m_pKeyboardHook != IntPtr.Zero)
            {
                switch (((Keys)m.vkCode))
                {
                    case Keys.LWin:
                    case Keys.Delete:
                    case Keys.Alt:
                    case Keys.F4:
                    case Keys.Control:
                    case Keys.Tab:
                        return 1;
                }
            }
            return 0;
        }