Well, the texture_env_combine extension is for video cards that don't support glsl... Only very old video cards can't support it (older than the nvidia tnt i think). What's your video card ? Try to skip the errors until they don't appear anymore (i stop displaying errors after a while) and see if it works. If your video card really doesn't support such extension, it means that you don't have any kind of multitexturing support which is of course required to emulate correctly the n64. Another thing, be sure you have installed the latest drivers for your video card.