RPC problems with sub window

I am new to Vaadin and I have created a simple application with a Tree Table launching a subwindow when an item is clicked. The subwindow has a text field and a “launch” button inside, and I can sucessfully read the data in the text field and the click on the launch button, but I cannot close the window.
I have setClosable(true) set in the window object and I have tried to close it manually using close() when the Launch button is clicked. When trying to close the window I get errors:

“…AM com.vaadin.server.communication.ServerRpcHandler parseInvocation
ADVERTENCIA: RPC call to v.v received for connector 4 but no such connector could be found. Resynchronizing client.”

My application is simple:

public class TradeSenseApp extends UI {
CSSFeeds cssFeeds = new CSSFeeds();
protected void init(VaadinRequest vaadinRequest) {
initLayout();
initFeeds();
}
private void initLayout() {
HorizontalSplitPanel splitPanel = new HorizontalSplitPanel();
setContent(splitPanel);
VerticalLayout leftLayout = new VerticalLayout();
splitPanel.addComponent(leftLayout);
//leftLayout.addComponent(bottomLeftLayout);
leftLayout.setSizeFull();
leftLayout.addComponent(tradeSenseModules);
}

private void initFeeds(){

//// I create the tree table and populate it ///

Below I create the listener for the click on the item in the tree table:
tradeSenseModules.addItemClickListener(new ItemClickEvent.ItemClickListener() {
public void itemClick(ItemClickEvent itemClickEvent) {
if (itemClickEvent.getItem().toString().equals(“Yahoo News”)){
UI.getCurrent().addWindow(cssFeeds);
} } });

In the CSSFeeds class I have:
public class TradeSenseApp extends UI {
public CSSFeeds(){
super(“Yahoo News”);
final FormLayout content = new FormLayout();
refreshTime = new TextField();
refreshTime.setImmediate(true);
refreshTime.setInputPrompt(“Refresh time (min)”);
refreshTime.setMaxLength(2);
content.setMargin(true);
setContent(content);
setClosable(true);
setWidth(400.0f, Sizeable.Unit.PIXELS);
Button launch = new Button(“Launch”);
launch.addClickListener(this);
content.addComponent(refreshTime);
content.addComponent(launch);}

public void buttonClick(Button.ClickEvent clickEvent) {
//Start / do / show some things.
close();
}

Any idea why I am getting these errors and why I cannot close the window either click on the X or with the close()?

I must be missing something obvious, when experimenting a bit more I added in my
init(VaadinRequest vaadinRequest) method:

Window test = new Window(“test”);
UI.getCurrent().addWindow(test);

The window can be closed (double clicking the X in the corner), but I am still getting:
WARNING: RPC call to v.v received for connector 1 but no such connector could be found. Resynchronizing client.
Apr 22, 2015 1:48:59 PM com.vaadin.server.communication.ServerRpcHandler parseInvocation