It looks like you just overwrote lxdm.conf during the upgrade with the defaults from upstream LXDM, instead of those from Lubuntu. There should have been a warning message saying that there were two different versions of that script, and which one you'd rather use, the current one or the package maintainer's version. It looks like you just chose the latter.
** Changed in: lxdm (Ubuntu) Status: Incomplete => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/823621 Title: Black screen at login To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lxdm/+bug/823621/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs