Communication problem Take note of any unsaved data, and click here to con

Vaadin 6 / 7 / 8
1

I run a simple example and everytime I want to see some interactions and see events run this pop-up appears
here is full spec of what I am doing :

There is an alredy deployed EJB , which has a WAR archive in it and I compile and upload compiled classes to “WEB-INF/classes/” automatically each time I make changes to my java classes.
I’ve uploaded vaadin *.jar files and other jar files according to the README file inside the vaading archive which I’ve downloaded from the site.
here are snapshots:

here is my directory listing :

the listing includes :

ant-1.6.5.jar
ant-launcher-1.6.5.jar
apache-mime4j-0.6.jar
appengine-api-1.0-sdk-1.2.1.jar
args4j-2.0.16.jar
atmosphere-compat-jbossweb-1.0.14.vaadin4.jar
atmosphere-compat-tomcat-1.0.14.vaadin4.jar
atmosphere-compat-tomcat7-1.0.14.vaadin4.jar
atmosphere-runtime-1.0.14.vaadin4.jar
commons-cli-1.2.jar
commons-codec-1.3.jar
commons-collections-3.1.jar
commons-io-2.2.jar
commons-jexl-2.1.1.jar
commons-lang-2.6.jar
commons-lang3-3.1.jar
commons-logging-1.1.1.jar
commons-math3-3.0.jar
cssparser-0.9.5.jar
guava-14.0.1.jar
hamcrest-core-1.3.jar
jetty-6.1.11.jar
jetty-util-6.1.11.jar
jsoup-1.6.3.jar
junit-4.11.jar
sac-1.3.jar
smartsprites-0.2.10.jar
swing-worker-1.1.jar
vaadin-client-compiled-7.1.7.jar
vaadin-client-compiler-deps-1.0.2.jar
vaadin-push-7.1.7.jar
vaadin-server-7.1.7.jar
vaadin-shared-7.1.7.jar
vaadin-shared-deps-1.0.2.jar
vaadin-slf4j-jdk14-1.6.1.jar
vaadin-theme-compiler-7.1.7.jar
vaadin-themes-7.1.7.jar
validation-api-1.0.0.GA-sources.jar
validation-api-1.0.0.GA.jar

and here is my web.xml file :

here is my simple Test Java Class:

package com.example;
import com.vaadin.event.ItemClickEvent;
import com.vaadin.ui.*;
import com.vaadin.server.VaadinRequest;


public  class PaperSubmissionApp extends UI {


    final Button bt = new Button("Push it!");
    final VerticalLayout vl = new VerticalLayout();
    @Override
    protected void init(VaadinRequest request) {

        setContent(vl);
        bt.addClickListener(new Button.ClickListener() {
            @Override
            public void buttonClick(Button.ClickEvent event) {
                bt.setCaption("You've Pushed It ");
            }
        });
        vl.addComponent(bt);

    }
}

everything seems fine by now but when I click the button the following happens:

I’m stuck and don’t know where to fix up!
Any Suggestion?
thanks for your time and sorry for too much details.