vaadin modal window probelm

Hi I have modal window i want to open another modal window on top of Modal window ,But it not taking ,it is showing an error saying like you can add window only application level window
how can i do it in other way Thanks in advance-_-

You can add as many as you like, but you just have to add them to an application level window and not to a sub window. Vaadin applications can have only one level of sub windows.