I have that problem too. It means that the mod you are trying too get does not work with Magiclauncher. I am looking everywhere to find a mod that works with it and so far i have found one and it is one this website. just search magiclauncher and then one result will pop up. Its lets you have different kinds of wolves like fire, ender, gold, diamond, etc. Its not exactly the most exciting mod, but its better than nothing.