Xenomatrix

Making a new world crashes the game. Minecraft launcher tells me this: The game crashed whilst ticking entity Error: java.lang.NoClassDefFoundError: com/pg85/otg/forge/dimensions/WorldProviderOTG

Currently, when I play on the forge profile, it doesn't save the world which I am playing on. I tried reinstalling Minecraft entirely, however that didn't work. I tried again on a superflat world (flew to a village and exited there) and it didn't save my position or my inventory. It worked perfectly on the unmodded profiles (or worlds). What is happening?