kubuntu upgrade 15.04 to 15.10 created an unresolvable problem

I did a complete

sudo apt-get update
sudo apt-get dist-upgrade

a couple of weeks after the release of Kubuntu 15.10, then tried the do-release-upgrade from within Muon updater.

I got the error messsage:

Could ot determine the upgrade

An unresolvable problem orrcured while calculating the upgrade.

I run Kubuntu and mythtv in lvm partitions on an mdadm RAID 5.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: ubuntu-release-upgrader-core 1:15.04.14.3
ProcVersionSignature: Ubuntu 3.19.0-32.37-lowlatency 3.19.8-ckt7
Uname: Linux 3.19.0-32-lowlatency x86_64
NonfreeKernelModules: nvidia tbs62x1fe tbs6982fe tbs6680fe tbs6923fe tbs6985se tbs6928se tbs6982se tbs6991fe tbs6618fe tbs6983fe tbs6922fe tbs6928fe tbs6991se tbs6290fe
ApportVersion: 2.17.2-0ubuntu1.7
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Fri Nov 6 20:49:30 2015
InstallationDate: Installed on 2012-09-15 (1147 days ago)
InstallationMedia: Kubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120423)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to vivid on 2015-11-06 (0 days ago)
VarLogDistupgradeTermlog: