do-release-upgrade crashed with TypeError in __init__(): wait_for_child() takes 1 positional argument but 2 were given

[Botan]

During installing "Ubuntu restricted extras" this error happened. My software updater is crashing.

ProblemType: Crash
DistroRelease: Ubuntu 15.04
Package: ubuntu-release-upgrader-core 1:15.04.13
ProcVersionSignature: Ubuntu 3.19.0-14.14-generic 3.19.3
Uname: Linux 3.19.0-14-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.1-0ubuntu1
Architecture: amd64
CrashDB: ubuntu
Date: Wed Apr 15 20:34:20 2015
ExecutablePath: /usr/bin/do-release-upgrade
InstallationDate: Installed on 2015-04-03 (11 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150326)
InterpreterPath: /usr/bin/python3.4
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/lib/ubuntu-release-upgrader/do-partial-upgrade --frontend=DistUpgradeViewGtk3
PythonArgs: ['/usr/bin/do-release-upgrade', '--frontend=DistUpgradeViewGtk3']
SourcePackage: ubuntu-release-upgrader
Title: do-release-upgrade crashed with TypeError in __init__(): wait_for_child() takes 1 positional argument but 2 were given
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

In the Traceback we can see the following:

SystemError: E:dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.

Have you tried running the suggested command?