Sharpdx DirectX11 MapSubresource is failing trying to map a staging texture

Question

I'm trying to render to a texture and then pull the image data out. I've created one texture as a render target and another as a staging texture. After rendering to the render target, I use CopyResource to copy from the render target texture to the staging texture. So far, so good. However, when I use DeviceContext.MapSubresource to get the data from the staging texture, I get E_INVALIDARGS exception, and I can't figure out why.

Here is how I create the staging texture:

        textureDesc = new Texture2DDescription()
        {
            ArraySize = 1,
            BindFlags = BindFlags.None,
            CpuAccessFlags = CpuAccessFlags.Read,
            Format = Format.B8G8R8A8_UNorm,
            Height = 256,
            MipLevels = 1,
            SampleDescription = new SampleDescription(1, 0),
            Usage = ResourceUsage.Staging,
            Width = 256
        };
        _renderStaging = new Texture2D(_dev, textureDesc);

Here is how I populate the staging texture and then try to map it:

            DataStream stream;
            _con.CopyResource(_renderTarget, _renderStaging);
            // The following is the line that fails
            box = _con.MapSubresource(_renderStaging, 0, MapMode.Read, MapFlags.None, out stream);

I have the same code working in C++, so I know I have the general idea right. This is the working C++ code:

textureDesc.Width = 256;
textureDesc.Height = 256;
textureDesc.MipLevels = 1;
textureDesc.ArraySize = 1;
textureDesc.Format = DXGI_FORMAT_B8G8R8A8_UNORM;
textureDesc.SampleDesc.Count = 1;
textureDesc.MiscFlags = 0;
textureDesc.Usage = D3D11_USAGE_STAGING;
textureDesc.BindFlags = 0; 
textureDesc.CPUAccessFlags = D3D10_CPU_ACCESS_READ;
hr = dev->CreateTexture2D(&textureDesc, NULL, &renderStagingTexture);

devcon->CopyResource(renderStagingTexture, renderTargetTextureMap);
D3D11_MAPPED_SUBRESOURCE mappedResource;
devcon->Map(renderStagingTexture, 0, D3D11_MAP_READ, 0, &mappedResource);

Answer 1

The error was due to _con being the deferred context while in the equivalent C++ code I was using the immediate context. When I switched the SharpDX code to use immediate context, it worked just as expected.

Unfortunately, the problem was not illustrated by the code I posted.