After several weeks of frustration following a failed reactivation process and installation (several times) of DS 2016 SP2 x64 (on Linux-Mint 18.3), I was finally able to get it to activate - by running it as root. Sounds like a solution? Well, not unless I want to have all of the files it creates (DWGs, DXFs, bitmaps, PDFs) also have root permission, and therefore unable to open them from my normal user account.
I have been able to get DS to install on Windows, but the interface uses the M\\\$ "ribbon" idea, and IO really don't have the time -or desire - to relearn.