I try to create simple java App on Heroku. I following step by step from http://samuelsharaf.wordpress.com/2011/11/06/create-a-simple-java-web-app-using-maven-and-upload-to-hero
Have you tried scaling one of your process types? e.g. heroku ps:scale web=1
heroku ps:scale web=1
Or rather, check what's your current web count by using 'heroku ps' See https://devcenter.heroku.com/articles/scaling