Explanation of the file format upgrade between AutoCAD 2017 & 2018
KeySCAPE and KeyTREE use Autodesk intelligent object technology. This allows us to provide the automatic changes you benefit from when using the software.
When Autodesk change the drawing format, as they did with the release of AutoCAD 2018, the Save As does not support backward compatibility of these objects and they can’t be edited within earlier versions. This is because, unlike simple and dumb AutoCAD elements, such as lines, text and hatch, the objects include new, intelligent information that earlier versions will not understand. This was most evident when AutoCAD introduced gradient fill hatches, where the Save As converted these back to solid hatches, losing drawing fidelity. To prevent similar degradation of information, Autodesk do not allow the intelligent objects (the ones we use for KeySCAPE and KeyTREE) to save back and downgrade. This means our features can be viewed as Proxy Entities in earlier versions but they not edited. Warnings are provided to this effect when opening older drawings and using Save As to earlier version of AutoCAD. This is not unique to our applications and Autodesk have similar issues with their own Civil 3D application, which uses the same object technology. See AutoCAD & AutoCAD Civil 3D 2018 Backwards Compatibility and Civil 3D Compatibility Matrix.
In response to customer requests and to meet the changing requirements of clients and the construction industry, from time to time we add features that older versions of KeySCAPE and KeyTREE would not understand the feature or how to edit them and the new features would be lost or degraded. Consequently, we are not always able to offer backward compatibility between the latest and earlier versions of KeySCAPE or KeyTREE.