taking screenshots from game environment using DirectX

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C#

DirectX

Hi,
I am trying to write a simple application that takes screenshots from games environment. I've search and based on my searches I need to use DirecX backbuffer. I tried to write some code, it works fine using frontbuffer that takes desktop screenshots, but when I use backbuffer and start a game to take pictures, it gives an error from Device() function saying : "Error in the application". How can I take screenshots from a game? what is wrong with this code?
Thanks.

Code:

PresentParameters pp = new PresentParameters();
pp.Windowed = true;
pp.SwapEffect = SwapEffect.Discard;
Device device = new Device(0, DeviceType.Hardware, this, CreateFlags.SoftwareVertexProcessing, pp);
Surface backbuffer = device.GetBackBuffer(0, 0, BackBufferType.Mono);
SurfaceLoader.Save("1.bmp", ImageFileFormat.Bmp, backbuffer);