ShowWindow can only be used for windows/controls which have a handle assigned. Elements don't return a handle (try it:
PlusWnd.GetControlHandle("FigRectNews") will return 0) and therefore you can't use API functions such as ShowWindow on it.
A work-around would be to place the Element in a child window, add the child to the parent window and hide the child window instead. But, if you want to make your window resizeable, you should add a message notification to the parent in order to make the child window resize too... but if you don't want a resizeable window, just forget this.
And in theory, this should be placed in the Scripts subforum.
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