Thanks a lot Brian it worked. removed kubuntu-backports and oibaf /graphics-drivers ppa using the ppa-purge then update issue was fixed and now upgraded to 18.04. Thanks again for your valuable time.
** Description changed: Update crashes with the screen: 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 + 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 ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: ubuntu-release-upgrader-core 1:16.04.25 ProcVersionSignature: Ubuntu 4.4.0-78.99-generic 4.4.62 Uname: Linux 4.4.0-78-generic x86_64 ApportVersion: 2.20.1-0ubuntu2.18 Architecture: amd64 CrashDB: ubuntu CurrentDesktop: KDE Date: Thu Aug 16 13:22:32 2018 InstallationDate: Installed on 2015-03-05 (1260 days ago) InstallationMedia: Ubuntu 12.04.5 LTS "Precise Pangolin" - Release amd64 (20140807) PackageArchitecture: all SourcePackage: ubuntu-release-upgrader UpgradeStatus: Upgraded to xenial on 2018-08-16 (0 days ago) VarLogDistupgradeTermlog: -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1787383 Title: Cant update Kubuntu 16.04 to 18.04 update crashes displaying "could not calculate the update" To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1787383/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
