There's probably another \0 character in the shader code before the end of file.

Why don't you try saving the shader in a text file, and open it inside the program and load the file to a buffer, and then try to compile it?

Try setting the file-name to NULL when you specify the code in memory.

Or try using D3DCompile instead. There's probably no reason to go through the D3DX11 function in this case.

I think the problem is that each "" pair in the HLSL dummy buffer is being treated as a single string, so each "" pair will have a \0 char at the end, hence the shader will stop compiling at the end of the first line.

Try this instead:

//Dummy hlsl code
    const char temp[] = {
                        "Texture2D colormap;\
                        Texture2D lightmap;\
                        \
                        SamplerState fullscreenQuadSampler;\
                        \
                        struct VertexInput\
                        {\
	                        float3 position : POSITION0;\
	                        float2 uv : TEXCOORD0;\
                        };\
                        \
                        struct PixelInput\
                        {\
	                        float4 position : SV_Position;\
	                        float2 uv : TEXCOORD0;\
                        };\
                        \
                        PixelInput VS(VertexInput input)\
                        {\
	                        PixelInput output;\
                            \
	                        output.position = float4(input.position, 1.0f);\
	                        float2 halfPixel = float2(0.5f / 800.0f, 0.5f / 600.0f);\
	                        output.uv = input.uv;// + halfPixel;\
                            \
	                        return output;\
                        }\
                        \
                        float4 PS(PixelInput input) : SV_Target\
                        {\
	                        float3 diffuseColor = colormap.Sample(fullscreenQuadSampler, input.uv).rgb;\
	                        float4 lightData = lightmap.Sample(fullscreenQuadSampler, input.uv);\
    \
	                        float3 diffuseLight = lightData.rgb;\
	                        float specularLight = lightData.a;\
                            \
	                        return float4(diffuseColor * diffuseLight + specularLight, 1.0f);\
                        }"
    };

Using the \ character at the end of the line indicates that the string continues on the next line, and there's no need to put each line in a "" pair.

Also, you could try what Erik Rufelt said. I don't use D3D so i don't know about it, but your problem, at least to me, seemed to be with the temp HLSL code.