I just did a fresh install of ubuntu-mate 16.04-alpha2, then I updated the kernel to 4.4.0-2-generic. Reboot, sudo apt-get update && sudo apt-get upgrade. And bingo, the error popped up.
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to lightdm in Ubuntu. https://bugs.launchpad.net/bugs/1542549 Title: package lightdm 1.17.5-0ubuntu2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1 Status in lightdm package in Ubuntu: Confirmed Bug description: desplay ProblemType: Package DistroRelease: Ubuntu 16.04 Package: lightdm 1.17.5-0ubuntu2 ProcVersionSignature: Ubuntu 4.4.0-3.17-generic 4.4.1 Uname: Linux 4.4.0-3-generic i686 ApportVersion: 2.19.4-0ubuntu2 Architecture: i386 Date: Sat Feb 6 00:30:33 2016 ErrorMessage: subprocess installed post-installation script returned error exit status 1 InstallationDate: Installed on 2016-02-04 (1 days ago) InstallationMedia: Ubuntu-MATE 16.04 LTS "Xenial Xerus" - Alpha i386 (20160127) RelatedPackageVersions: dpkg 1.18.4ubuntu1 apt 1.1.10 SourcePackage: lightdm Title: package lightdm 1.17.5-0ubuntu2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1 UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1542549/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp