Upgrade of TDE DVD 14.04 to 16.04 -- FAIL

I've just installed the Trinity LiveCD tde-ubuntu-14.04-desktop-r14.0.3-amd64.iso and performed all the updates. I commented out the entries in /etc/apt/sources.list.d/libreoffice-trinity.list -and- /etc/apt/sources.list.d/trinity.list and did a sudo do-release-upgrade to upgrade to xenial (16.04) and received the following: |Checking package manager |Reading package lists... Done |Building dependency tree |Reading state information... Done |Building data structures... Done | |Calculating the changes| | |Calculating the changes | |Could not calculate the upgrade | |An unresolvable problem occurred while calculating the upgrade. | |This can be caused by: |* Upgrading to a pre-release version of Ubuntu |* Running the current pre-release version of Ubuntu |* Unofficial software packages not provided by Ubuntu | |If none of this applies, then please report this bug using the |command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. | |Restoring original system state | |Aborting I don't see how any of the "This can be caused by" pertain. I have done this process successfully with the _32bit_ Trinity LiveCD Where to start? Jonesy -- Marvin L Jones | Marvin | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | FreeBSD __ 38.238N 104.547W | jonz.net | DM78rf | OS/2 SK