hWndPreview = Trim(Right(strArguments, Len(strArguments) - 2))

is that the actual object.hWnd of the Preview window? You're passing a string to a Long, try this instead

hWndPreview = CLng(Trim(Right$(strArguments, Len(strArguments) -2)))

MsgBox ("There are no configuration settings for this screensaver.") 'this is specifying a Function, Remove the parenthesis and this part will work correctly. You'll get a runtime error if you don't.

MsgBox "There are no configuration settings for this screensaver."