[Bug 1232700] [NEW] failed to calculate the upgrade of the system

[stah007]

Public bug reported:

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

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1232700

Title:
  failed to calculate the upgrade of the system

Status in “ubuntu-release-upgrader” package in Ubuntu:
  New

Bug description:
  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

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