Hooray! This is progress! The behavior you describe is, shall we say, counter-intuitive? Bravo for pressing ahead anyway.

Source: PinPoint.Plate
Message: The value is out of range.: ArcsecPerPixelHoriz

I'm going to guess at this one. Check the focal length in ACP's Preferences, Telescope window. If the plate scale is way off, then the focal length is probably way off. If not then I will need to dig deeper.