Comment 97 for bug 969489

This happens sometimes on my machine:
Ubuntu 12.04 64bit
Intel SSD 335
Nvidia GTS 650 with NVIDIA drivers.
lightdm version 1.2.3-0ubuntu2.3

Tracked it to a race issue - if NVRM module is loaded before lightdm starts, all is OK. (see logs in Post Scriptum)

My current configuration in /etc/init/lightdm.conf:

start on ((filesystem
           and runlevel [!06]
           and started dbus
           and plymouth-ready)
          or runlevel PREVLEVEL=S)

Post Scriptum: Logs clearly showing that when lightdm is started before the NVRM module is loaded, and dies a horrible death:
Sep 13 14:20:07 Pendragon kernel: [ 5.944960] ADDRCONF(NETDEV_UP): wlan0: link is not ready
Sep 13 14:20:07 Pendragon kernel: [ 6.099801] init: lightdm main process (1127) terminated with status 1
Sep 13 14:20:07 Pendragon kernel: [ 6.509805] HDMI status: Codec=0 Pin=5 Presence_Detect=0 ELD_Valid=0
Sep 13 14:20:07 Pendragon kernel: [ 6.533772] HDMI status: Codec=1 Pin=5 Presence_Detect=0 ELD_Valid=0
Sep 13 14:20:07 Pendragon kernel: [ 6.557710] HDMI status: Codec=2 Pin=5 Presence_Detect=0 ELD_Valid=0
Sep 13 14:20:08 Pendragon kernel: [ 6.581717] HDMI status: Codec=3 Pin=5 Presence_Detect=0 ELD_Valid=0
Sep 13 14:20:08 Pendragon kernel: [ 6.581814] input: HDA NVidia HDMI/DP,pcm=9 as /devices/pci0000:00/0000:00:03.0/0000:01:00.1/sound/card1/input10
Sep 13 14:20:08 Pendragon kernel: [ 6.581890] input: HDA NVidia HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:03.0/0000:01:00.1/sound/card1/input11
Sep 13 14:20:08 Pendragon kernel: [ 6.581954] input: HDA NVidia HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:03.0/0000:01:00.1/sound/card1/input12
Sep 13 14:20:08 Pendragon kernel: [ 6.582180] input: HDA NVidia HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:03.0/0000:01:00.1/sound/card1/input13
Sep 13 14:20:08 Pendragon kernel: [ 6.583236] nvidia 0000:01:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
Sep 13 14:20:08 Pendragon kernel: [ 6.583243] nvidia 0000:01:00.0: setting latency timer to 64
Sep 13 14:20:08 Pendragon kernel: [ 6.583247] vgaarb: device changed decodes: PCI:0000:01:00.0,olddecodes=io+mem,decodes=none:owns=io+mem
Sep 13 14:20:08 Pendragon kernel: [ 6.583341] NVRM: loading NVIDIA UNIX x86_64 Kernel Module 319.32 Wed Jun 19 15:51:20 PDT 2013
Sep 13 14:20:08 Pendragon kernel: [ 6.794290] init: udev-fallback-graphics main process (1380) terminated with status 1
Sep 13 14:20:08 Pendragon kernel: [ 6.951100] init: plymouth-stop pre-start process (1400) terminated with status 1
Sep 13 14:20:08 Pendragon kernel: [ 7.533643] cfg80211: Found new beacon on frequency: 2472 MHz (Ch 13) on phy0