Sender is the event handler control.
Window is the unexpected window object. This may be your best bet to find the text/caption on the alert box. You can add the follow to find the full name of the unexpected window:
Log.Message("Unexpected Window: " & Window.FullName)
LogParams contains the detail and information on the message TC is about to post to the log.
To answer your third question, find that windows property and check if it contains the text you're looking for. If the window object does not contain the text, check the Object Browser in TestComplete while the unexpected window is onscreen. See which object contains the text you're looking for. Then compare using that.
Cheers,
Jackson
