By Andy Davis
If you are trying to install the AutoCAD Plant 3D 2019 Object Enabler for Navisworks 2019 side-by-side with the 2018 or 2017 versions, the installer may report that a previous version is already installed and then fail.
The solution to this problem is to uninstall the 2017 and 2018 versions of the Object Enabler before installing the 2019 version.
Once the 2019 version has been installed, the 2017 and 2018 versions may be re-installed.