Comment 13 for bug 412113

I am also having this problem (on karmic) . Xorg log says:

Backtrace:
0: /usr/bin/X(xorg_backtrace+0x3b) [0x8133d6b]
1: /usr/bin/X(xf86SigHandler+0x55) [0x80c7d35]
2: [0xa5a400]
Saw signal 11. Server aborting.
(II) Power Button: Close
(II) UnloadModule: "evdev"
(II) AT Translated Set 2 keyboard: Close
(II) UnloadModule: "evdev"
(II) Power Button: Close
(II) UnloadModule: "evdev"
(II) Macintosh mouse button emulation: Close
(II) UnloadModule: "evdev"
(II) Logitech USB-PS/2 Optical Mouse: Close
(II) UnloadModule: "evdev"
 ddxSigGiveUp: Closing log

on the syslog I find:

Nov 27 11:20:53 mogul acpid: client 1559[0:0] has disconnected
Nov 27 11:20:53 mogul acpid: client 1559[0:0] has disconnected
Nov 27 11:20:53 mogul acpid: client connected from 22729[0:0]
Nov 27 11:20:54 mogul acpid: client connected from 22729[0:0]
Nov 27 11:24:54 mogul acpid: client 22729[0:0] has disconnected
Nov 27 11:24:54 mogul acpid: client 22729[0:0] has disconnected
Nov 27 11:24:54 mogul acpid: client connected from 22729[0:0]
Nov 27 11:24:54 mogul acpid: client connected from 22729[0:0]

my video card:
01:00.0 VGA compatible controller: nVidia Corporation NV44 [Quadro NVS 285] (rev a1)
ii nvidia-glx-185 185.18.36-0ubuntu9 NVIDIA binary Xorg driver

When this happens, X crashes and then I am presented the login screen again...