The problem lies in the fact that you're trying to use some kind of menu identifier as window identifier.
In your JScript:
js code:
WndNew = MsgPlus.CreateWnd("New.xml", "mnuNew");
In your interfaces XML:
xml code:
<Window Id="options" Version="1">
The "mnuNew" should be replaced by "options" so that Plus! can find the right window to load. Same goes for the about window: you defined it as "About" in your interfaces but you try to open "mnuAbout".
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