[SOLVED] GWT Designer doesn't work

I'm using:

Eclipse Kepler 4.3 JDK 7 GWT compatible with eclipse 4.3 (downloaded via market place) GWT version is downloaded via market place with GWT by default 2.6.0 On eclipse the java compiler version is 1.7 It's not a maven project

When I try do open the GWT EntryPoint class (that is a UI) it throws the bellow error:

The EntryPoint class (the default created by eclipse when creating a new GWT Project):

package xsdf.com.client;

import xsdf.com.shared.FieldVerifier;

/**
 * Entry point classes define <code>onModuleLoad()</code>.
 */
public class Xxwa implements EntryPoint {
    /**
     * The message displayed to the user when the server cannot be reached or
     * returns an error.
     */
    private static final String SERVER_ERROR = "An error occurred while "
            + "attempting to contact the server. Please check your network "
            + "connection and try again.";

    /**
     * Create a remote service proxy to talk to the server-side Greeting service.
     */
    private final GreetingServiceAsync greetingService = GWT
            .create(GreetingService.class);

    /**
     * This is the entry point method.
     */
    public void onModuleLoad() {
        final Button sendButton = new Button("Send");
        final TextBox nameField = new TextBox();
        nameField.setText("GWT User");
        final Label errorLabel = new Label();

        // We can add style names to widgets
        sendButton.addStyleName("sendButton");

        // Add the nameField and sendButton to the RootPanel
        // Use RootPanel.get() to get the entire body element
        RootPanel.get("nameFieldContainer").add(nameField);
        RootPanel.get("sendButtonContainer").add(sendButton);
        RootPanel.get("errorLabelContainer").add(errorLabel);

        // Focus the cursor on the name field when the app loads
        nameField.setFocus(true);
        nameField.selectAll();

        // Create the popup dialog box
        final DialogBox dialogBox = new DialogBox();
        dialogBox.setText("Remote Procedure Call");
        dialogBox.setAnimationEnabled(true);
        final Button closeButton = new Button("Close");
        // We can set the id of a widget by accessing its Element
        closeButton.getElement().setId("closeButton");
        final Label textToServerLabel = new Label();
        final HTML serverResponseLabel = new HTML();
        VerticalPanel dialogVPanel = new VerticalPanel();
        dialogVPanel.addStyleName("dialogVPanel");
        dialogVPanel.add(new HTML("<b>Sending name to the server:</b>"));
        dialogVPanel.add(textToServerLabel);
        dialogVPanel.add(new HTML("<br><b>Server replies:</b>"));
        dialogVPanel.add(serverResponseLabel);
        dialogVPanel.setHorizontalAlignment(VerticalPanel.ALIGN_RIGHT);
        dialogVPanel.add(closeButton);
        dialogBox.setWidget(dialogVPanel);

        // Add a handler to close the DialogBox
        closeButton.addClickHandler(new ClickHandler() {
            public void onClick(ClickEvent event) {
                dialogBox.hide();
                sendButton.setEnabled(true);
                sendButton.setFocus(true);
            }
        });

        // Create a handler for the sendButton and nameField
        class MyHandler implements ClickHandler, KeyUpHandler {
            /**
             * Fired when the user clicks on the sendButton.
             */
            public void onClick(ClickEvent event) {
                sendNameToServer();
            }

            /**
             * Fired when the user types in the nameField.
             */
            public void onKeyUp(KeyUpEvent event) {
                if (event.getNativeKeyCode() == KeyCodes.KEY_ENTER) {
                    sendNameToServer();
                }
            }

            /**
             * Send the name from the nameField to the server and wait for a response.
             */
            private void sendNameToServer() {
                // First, we validate the input.
                errorLabel.setText("");
                String textToServer = nameField.getText();
                if (!FieldVerifier.isValidName(textToServer)) {
                    errorLabel.setText("Please enter at least four characters");
                    return;
                }

                // Then, we send the input to the server.
                sendButton.setEnabled(false);
                textToServerLabel.setText(textToServer);
                serverResponseLabel.setText("");
                greetingService.greetServer(textToServer,
                        new AsyncCallback<String>() {
                            public void onFailure(Throwable caught) {
                                // Show the RPC error message to the user
                                dialogBox
                                        .setText("Remote Procedure Call - Failure");
                                serverResponseLabel
                                        .addStyleName("serverResponseLabelError");
                                serverResponseLabel.setHTML(SERVER_ERROR);
                                dialogBox.center();
                                closeButton.setFocus(true);
                            }

                            public void onSuccess(String result) {
                                dialogBox.setText("Remote Procedure Call");
                                serverResponseLabel
                                        .removeStyleName("serverResponseLabelError");
                                serverResponseLabel.setHTML(result);
                                dialogBox.center();
                                closeButton.setFocus(true);
                            }
                        });
            }
        }

        // Add a handler to send the name to the server
        MyHandler handler = new MyHandler();
        sendButton.addClickHandler(handler);
        nameField.addKeyUpHandler(handler);
    }
}

The error when I try to open the above class with GWT Designer:

 Internal Error
encountered unexpected internal error. 

This could be caused by a bug or by a misconfiguration issue, conflict, partial update, etc.

java.lang.NoSuchMethodError: com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(Lcom/google/gwt/core/ext/TreeLogger;Ljava/lang/String;Z)Lcom/google/gwt/dev/cfg/ModuleDef;



Show stack trace. 
Hide stack trace. 

Stack trace:
java.lang.NoSuchMethodError: com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(Lcom/google/gwt/core/ext/TreeLogger;Ljava/lang/String;Z)Lcom/google/gwt/dev/cfg/ModuleDef;
    at com.google.gwt.dev.shell.designtime.HostedModeSupportImpl.loadModule(HostedModeSupportImpl.java:85)
    at com.google.gwt.dev.shell.designtime.HostedModeSupportImpl.createModuleSpaceHost(HostedModeSupportImpl.java:64)
    at sun.reflect.NativeMetho

I already checked the possible problems of:

What should I do if I encounter an NoSuchMethodError or NoClassDefFoundError using GWT Designer?

https://developers.google.com/web-toolkit/tools/gwtdesigner/faq#NoSuchMethodError

I already tried different vms, 1.8, 1.6;

Does GWT Designer is still ative? Is the better option to design UI? How to correct this error and make GWT Designer to work properly?