It kindof wrecked my nerves: In order to migrate from 2.8 upwards, it seems that the folder
.ganttproject.d as well as the old .ganttproject file need to be removed prior to the installation
of version three. Is it possible that the installer does it itself, please !!!
Before 3.0 there was no .ganttproject.d folder on Windows. Options file is usually compatible, at least I am not aware of any specific reasons of incompatibility. There are thousands of users for whom migration went smoothly. So, no, removing user settings automatically is probably not the best idea.