Glladstone Gamer

Today i installed forge 1.8.9 and the weather mod, but, every time i play with the forge, an error ocurs, my minecraft crash and show this message on my screen. The game crashed whilst there was a severe problem during mod loading that has caused the game to fail The game crashed whilst there was a severe problem during mod loading that has caused the game to fail Error: net.minecraftforge.fml.common.LoaderException: java.lang.NoClassDefFoundError: modconfig/IConfigCategory. Please help me!!! I really want to use the mod, and i can't because of the mistake.