I just downloaded Minecraft today on my MacBook Air, but for some reasons, whenever I click Play, it kept on repeating this error message that says "Sorry,unable to start Minecraft.Please check your configuration. My friend kept asking me if I knew the version, and told be that the version number should be in the down left menu, but I don't have it. I am so confused, and I don't know what to do. And yes, I do not know the version.