Ive found one thread on a german forum with exact the same issue. The user from there had a chunkloader too in the nether and a normal big city on the overworld, and since few restarts and ore replacing (i can remember i retrogenerate few times after the first clear install. Now i have it, i think i know from where the error comes. I have created my first world with 1.0.4, and updated the thermal expansion pack like the topic (http://forum.feed-the-beast.com/thr...d-before-updating-any-pack.36499/#post-503482) and then i retrogenerated the ore and restarted him several times, and then 1.0.5 appears and i updated the server and done now again some retrogens and i think thats the issue... Like the guy in the german forums mean to often stop/restard can leak something, i think my world doesnt survived that how often i maked that. I try it now with a clear install/world delete/to let my fingers away from ore config/retrogen and tell you if the error appears again. My next question is can i use the biomesoplenty mod for generating the world? when yes is the command level-type=BIOMESOP right? Many Thanks!