Ruby : Internal Server Error

The sever show me this message as following ,

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@localhost and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.
Apache/2.2.12 (Ubuntu) Server at 127.0.1.1 Port 80

then i check the apache log at /var/log/apache2/error.log like this

warning: Insecure world writable dir /var/www in LOAD_PATH, mode 040777
Jun 28 23:05:34 2011] [error] mod_ruby: error in ruby
Jun 28 23:05:34 2011] [error] mod_ruby: /usr/lib/ruby/1.8/apache/ruby-run.rb:53:in `load': loadin
Jun 28 23:05:34 2011] [error] mod_ruby:   from /usr/lib/ruby/1.8/apache/ruby-run.rb:53:in `handle

Now,  i setting the directory /var/www/   by this command : 

sudo chmod go-w /var/www

it works .