Hello Afroz,

It would have helped if you had also attached code, because at this point I can only guess whether the ContentTemplate or an external page is used for the RadWindow content and the exact issue is not very clear from the cropped screenshot.
At this point I would advise that you examine this demo on a similar scenario: http://demos.telerik.com/aspnet-ajax/editor/examples/editorinradwindow/defaultcs.aspx.

If this does not work for you I can suggest trying to restore the RadEditor when the RadWindow is minimized (use its OnClientCommand event) and maximize the editor again when the window is restored.
If you are using an external page things should be OK, but still you can create functions in it that will toggle the editor's full screen mode and call them as shown here. You can use the toggleScreenMode() method RadEditor exposes for that. You can also try calling its repaint() method instead to see if this helps.


Regards,
Marin Bratanov
Telerik