RTMP requires a unique port to run - this port is independent of the HTTP port used by the web server. Check your /WEB-INF/flex/server-config.xml file and ensure that each RTMPChannel based channel-definition uses a unique port across any J2EE app on the entire server.
Is there any way to use rtmp connectivity in cases when I have access to internet only via proxy and only 80 port is avaliable for me?
Wow - this is an old thread....
Short answer: Maybe.
If you can run the RTMP channel on port 80 and your proxy doesn't try to cache or buffer requests, then yes you can use RTMP. If you are sharing the machine with a web server that is already listening on port 80, then you will have to use one of the other HTTP servlet based channels.
See this discussion of the types available: http://www.dcooper.org/blog/client/index.cfm?mode=entry&entry=8E1439AD-4E22-1671-58710DD52 8E9C2E7