Using the GUI Updater which has always showed "Upgrade available" but I have ignored it -- up until today. :) Then got the errors.
The only two packages that I am aware of are BackInTime (BiT) and Wine and both have their PPAs defined and checked. After the first go around of errors I disabled the PPAs for Wine and BiT and the ERROR1 message went away, but still got ERROR 2.
I tried this but same again... Can't upgrade from 12.04LTS to 14.04LTS
How do I do the Upgrade? OR, is there some way to push all my 14.04 programs and data over to a clean install of 16.04?
ERROR 1: Preparing to Upgrade
Third party sources disabled Some third party entries in your sources.list were disabled. You can re-enable them after the upgrade with the 'software-properties' tool or your package manager.
ERROR2: Setting new software channels
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.