Try opening world from a command prompt and see if it spits out an error. However, it's probably a problem with your configuration file somehwere. Make sure your brackets are all closed, are in the right place/format, and watch what you use to edit the file. Use notepad if you can as that adds no additional format marks and such. If you're under Linux, doesn't use gedit
I learned that myself.
I would start with a fresh config file from the wiki and slowly edit it, starting world with every change until you are through.