I am getting a really weird error every time I create a new world or load an existing one that says a backup level.dat is being used (hence the really weird... shouldn't even be a backup on creation of a new world). I decided to load with just Forge and no mods to see if it persisted; it did. I do use Curse to launch my game, but since it uses the native minecraft launcher that shouldn't be an issue. I have no clue what is causing this. The file in question isn't read-only or anything. I can still load created world or reload saved ones despite the error, but I worry that it will cause other problems and wanted to make sure the devs were aware of this in case it is something wrong with Forge. Here is a gist with my latest.log after starting to create a new world but saying no so it wouldn't load the world when it threw the error: https://gist.github.com/Dragnier/538665bec9f5d1e49a666f7521d2eea7