I use LiteLoader and forge. There is a particular mod maker who claims that "mixins" error is from forge not LiteLoader.
http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2469613-controlpack-many-useful-features-such-as-automine?page=2
That is the topic and page where the mod author says it is related to forge.
I really like the mod so I was hoping if i posted it, I can find out if it's really a forge error.