system out of memory when trying to saveAsPng

Hi first of I create my rendertarget2D

_canvas = new RenderTarget2D(_device, _canvasSize, _canvasSize);

Then I try and save it

using (FileStream stream = File.Create("texturepack" + _canvasSize.ToString()))
            {
                _canvas.SaveAsPng(stream, _canvasSize, _canvasSize);
            }

at this point the memory jumps up to just over 700mbs then I get System.OutOFMemoryException

What I don’t understand is I have both 8gb of system memory and 8gb of gpu memory
Now the texture is massive 8192x8192 but still I shouldn’t be getting this error when I have over 3 gb of memory free.

Any help would be apricated

EDIT: running windows directX and using HiDef profile

I’m not sure if this will help but have a search for “C# Large address aware”.

I’ve used it in non-gaming related software to applications that were using too much RAM.

It may help you out.

Thank you so much, just had to build for x64 and it worked perfectly.
thanks