I am using GWT. have below code in my host page.

```
<div id="mainDiv"/>
 <iframe id="__printingFrame" style="width:0;height:0;border:0"> </iframe> 

```

in EntryPoint's onModuleLoad() i have below code:

```
@Override
    public void onModuleLoad() {
        RootPanel.get("mainDiv").add(new SomePage());
    }

```

in one of the methods of SomePage.java i am doing:

```
RootPanel rootPanel = RootPanel.get("__printingFrame");
  rootPanel.add(new Html(" "));//adding some widget

```

But bcaz of above line i am getting below exception. Am i missing anything here?

```
java.lang.AssertionError: A widget that has an existing parent widget may not be added to the detach list
    at com.google.gwt.user.client.ui.RootPanel.detachOnWindowClose(RootPanel.java:136)
    at com.google.gwt.user.client.ui.RootPanel.get(RootPanel.java:211)

```

Thanks!