Usually when I get the premature end of header error, I’ve been able to load up script/console and it will crash with a more robust error message letting me know that I’ve forgotten some code in config/environment.rb. If you’re not getting an error with Webrick, I’m not sure. But I’d start looking around in config/environment.rb. It seems that any problems in that file never make it to a non-Apache log whereas bugs in other files are written to the appropriate RAILS_ENV mode log file. Does that help?