Chickenchunks 1.2.1.1 and Forge Build 6.6.0.516 - Forge Build 6.6.0.518 dont play nice together
09:02:20 [sEVERE] [ForgeModLoader] Detected leaking worlds in memory. There are 4 worlds that appear to be persisting. A mod is likely caching the world incorrectly
09:02:20 [sEVERE] [ForgeModLoader] The world 69cf291a (world) has leaked.
09:02:20 [sEVERE] [ForgeModLoader] The world 6b54afba (world) has leaked.
Build 6.6.0.515 works fine doh.