Why "IllegalStateException: !(Jetty || Servlet 3.0 || ContinuationFilter)" is thrown ?

The CometD implementation relies on Jetty Continuations.
This exception is thrown by the Jetty Continuation library when it finds that the web application configuration is not correct for the library to work.

To run properly, web applications that make use of this library needs either:

• to run inside Jetty 6 or Jetty 7
• to run in a Servlet 3.0 compliant servlet container
• to have the ContinuationFilter configured properly

See here for details on configuring the ContinuationFilter.