Connection to the client address X.X.X.X:YYYY is not allowed

If you get this error when you're trying to start debug session, it means that debugger module on that server is not configured or intentionally prohibit you from running debug sessions.
You may want to check debugger settings in php.ini. To allow host X.X.X.X:YYYY to run debug sessions you need the following settings:
debugger.hosts_allow=X.X.X.X
debugger.ports=YYYY
See this post for further details http://forum.nusphere.com/howto-install-debugger-module-t576.html