errors while upgrade from 16.04 to 18.04

[gkbatchelor]

command:sudo do-release-upgrade
正在计算变更

正在计算变更

无法计算升级

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

如果这些都不生效，请在终端中使用命令 'ubuntu-bug ubuntu-release-upgrader-core' 来报告
bug。If you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.29
ProcVersionSignature: Ubuntu 4.15.0-72.81~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-72-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue Dec 3 07:46:30 2019
InstallationDate: Installed on 2019-10-28 (35 days ago)
InstallationMedia: Ubuntu 16.04.6 LTS "Xenial Xerus" - Release amd64 (20190227)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2019-12-02 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2019-12-03T07:38:36.791583