"Specified element is already the logical child of another element. Disconnect if first."
The error was due to, at the first time population of stack panel went happily
but at the second time when I tried to populate the global content to the stack panel, the previous instance of stack panel still holds the global content and prevented me to populate the same content further and caused an exception.
I tried lot many workarounds for populating the stack panel the second time and later found the solution to be too simple.
In Page_1.xaml I created Closing = "Window_Closing" event. This event will be fired when the current window is closed. In this event I cleared the stack panel
so no more global content will be there before I go to new window(Page_2.xaml). Now if I go back to the Page_1.xaml the population of stack panel will happen with no exception as the contents are already cleared.