C# と VB.NET の質問掲示板

すいません、Win10だとうまくいったのですが、
Win7でやると
DwmGetWindowAttributeで値を取得することができません。
特にエラーは出ないのですが、座標が全て0になってしまいます。
どうすれば良いですか？

コードは以下の通りです。


    Private Enum DWMWINDOWATTRIBUTE
        DWMWA_NCRENDERING_ENABLED = 1
        DWMWA_NCRENDERING_POLICY
        DWMWA_TRANSITIONS_FORCEDISABLED
        DWMWA_ALLOW_NCPAINT
        DWMWA_CAPTION_BUTTON_BOUNDS
        DWMWA_NONCLIENT_RTL_LAYOUT
        DWMWA_FORCE_ICONIC_REPRESENTATION
        DWMWA_FLIP3D_POLICY
        DWMWA_EXTENDED_FRAME_BOUNDS
        DWMWA_LAST
    End Enum
    Private Declare Function DwmGetWindowAttribute Lib "dwmapi.dll" (
     ByVal hwnd As IntPtr,
     ByVal dwAttribute As DWMWINDOWATTRIBUTE,
     ByRef pvAttribute As RECT,
     ByVal cbAttribute As Int32) As Boolean

    Private Structure RECT
        Property Left As Integer
        Property Top As Integer
        Property Right As Integer
        Property Bottom As Integer
    End Structure




            Dim wombat As RECT
            DwmGetWindowAttribute(frm.Handle, DWMWINDOWATTRIBUTE.DWMWA_EXTENDED_FRAME_BOUNDS, wombat, Marshal.SizeOf(wombat))

            Dim bmp As New Bitmap(wombat.Right - wombat.Left, wombat.Bottom - wombat.Top)

            Dim g As Graphics = Graphics.FromImage(bmp)

            g.CopyFromScreen(New Point(wombat.Left, wombat.Top), New Point(0, 0), bmp.Size)
            g.Dispose()

            bmp.Save(FileOutPath_PNG)
            bmp.Dispose()