I don't really know Cg, but if tex2D is equivalent to what it was in older HLSL then you can't use it anything except for a pixel shader. This is because it uses screen-space gradients to automatically select the mip level, and gradients can only be computed in a pixel shader. Try using tex2Dlod, or whatever the Cg equivalent is for a function that lets you manually specify the mip level.

Have you confirmed that 'texUV' is a float2.

It seems that for tex2Dlod, you'd have to use float4 for 'texUV' //=================================================================== sampler2D samp; float4 tex2Dlod(sampler2D samp, float4 s)// s.w selects the mipmap level //=================================================================== http://http.developer.nvidia.com/Cg/tex2Dlod.html //=================================================================== And it says at the bottom that your GPU must support the vp40 profile. If you have a decent video card this should not be a problem. I suspect a lot of laptops might not support this.