I have tried all kind of solutions but I still can't upload my own world. I tried to upload it on both server console and in-game. I get the error "undefined" in server console. However, it says "downloading X MB file" with the /ul world command in game but it never ends so nothing happens. The only thing that I can upload is the level.dat file but it just creates the default world, there is no my buildings etc. Please tell me how to solve this problem. At least give me a world file to upload. I really don't understand what's the issue.