Just like it says in the title, I followed heroku's [instructions](http://devcenter.heroku.com/articles/custom-domains) and added 'myapp.com' and 'www.myapp.com' as domains for my heroku app. 

The former works correctly but the latter does not. Any ideas? EDIT: When I point my browser to 'www.myapp.com', I get an error from Comcast, my ISP, saying that the URL was not found.