First, make sure your system is in non-sequential mode before opening the Detector Viewer.  You can use TheSystem.MakeNonSequential().

You can use either New_DetectorViewer() or New_Analysis(); underneath the hood, these are the exact same method with the ZOS-API.  I personally like using New_Analysis_SettingsFirst() since this will open the analysis without running it first (there are some long-running analysis like POP that this could make a difference).

As for the settings, you should use DetectorView.GetSettings().  The IAS_DetectorViewer is an interface and cannot be used like a method.  If you’re using Python, it’s always a good idea to cast the parent implementation of the setting via DetectorView.GetSettings().__implementation__ (this will inherent any methods from the IAS_ parent interface like Field, Wavelength or Surface if the analysis has these implemented).

Finally, the ZRD file should be in the same folder as the non-sequential ZMX file.  If you haven’t loaded a ZMX file, then the default folder will be Documents\Zemax\Samples.