Run "mvn:dependency tree" from the command line and make sure your dependencies match the table here http://tapestry-atmosphere.uklance.cloudbees.net/. You might need to <exclude> a dependency? Not sure.
I had troubles with tomcat and apache on cloudbees and had to upgrade to http 1.1. Does it work on jetty (runjettyrun plugin?). Possibly best to ask further questions on atmosphere users list if it's more relevant there.
