Thanks for the info. It shouldn't be a problem since I coded it to use OpenGL 2.1 and GLSL 1.2, which is pretty old and should be compatible with most old cards. All I can think of is maybe you need to check if you have the newest drivers for your graphics card?
Either way, I'll look around on some forums and see if anyone has mentioned similar issues with AMD and the way I've written the renderer.
Sorry I couldn't fix it right away, but you've been very helpful.