If the HtmlWindow has been closed by the user or by way of a call to the Close method, attempting to navigate to a new URL or access the window's document will result in an error. Use this property to determine whether it is safe to call properties and methods on the current window object.
The following code example opens a window, and closes it if the user has not used it in the past five minutes. The code example requires that your form has a WebBrowser control named WebBrowser1, a Button named Button1, and a Timer class named Timer1.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)