Snapshot of any window in foreground? Similar to Task Switcher

Title is self explainatory.
Here is the code:

Code:

---

        public Bitmap CaptureWindow(IntPtr hWnd)
        {


            Rectangle rctForm = Rectangle.Empty;
            IntPtr test = GetWindowDC(hWnd);
            Graphics grfx = Graphics.FromHdc(test);
            using (grfx)
            {
                RectangleF test2 = grfx.VisibleClipBounds;
                rctForm = Rectangle.Round(grfx.VisibleClipBounds);
            }

            Bitmap pImage = new Bitmap(rctForm.Width, rctForm.Height);
            Graphics graphics = Graphics.FromImage(pImage);

            IntPtr hDC = graphics.GetHdc();
            //paint control onto graphics using provided options       
            try
            {
                PrintWindow(hWnd, hDC, (uint)0);
            }
            finally
            {
                graphics.ReleaseHdc(hDC);
            }
            return pImage;
        }

---

Now... It works for most of the windows but not all. Example: http://snpr.cm/ozRClN.jpg
Non working: http://snpr.cm/HU2QuR.jpg. Its a Delphi program but i guess it doesnt matter. Same happens to few others.

The function is called in on Load event of my Form containing PictureBox

Code:

---

pictureBox1.Image = CaptureWindow(okienko);

---

'okienko' is a handle to that window.

I already tested out few solutions using gdi32.dll and user32.dll functions but without luck.

Facts:
1.What i have already discovered is different property of 'Graphics grfx = Graphics.FromHdc(test);'

2.Working thumbnails has "IsVisibleClipEmpty" property set to false, while blank ones are true values.
Screenshot: http://snpr.cm/vGytAV.jpg

3.Function returns in this line each time it crashes:

Code:

---

rctForm = Rectangle.Round(grfx.VisibleClipBounds);

---

Im also curious how did they manage to do it in win7(alt-tab task switcher)? Do you have any clues mighty gurus? What could possibly set the IsVisibleClipEmpty property to true if i can get the handle to the window and see the content with my own eyes? Why is it blind for some windows and then miraculously cured the other second on?