Exception has occured...

I'm getting an exception thrown when I try to run a test scene following this example. Here is what it's saying to me:

Error #9
Function: CgProgram::loadFromSource
Description: Unable to compile Cg program BasicTexture_PS: CG ERROR: The compile returned an error.
(20):error C1008: undefined variable "diffuse"
(20):error C1115: unable to find compatible overloaded function "tex2d"

I know it's because "diffuse" wasn't defined, I just don't know how to do it. I can see in the example code it's referenced, but not defined. Please fix this!