BUG: unable to handle kernel NULL pointer dereference at (null) [netlink_proto+0x0/0xc0]

When the computer is idle and the screen turns off the system doesn't respond anymore. You can't start any OS after this.

ProblemType: KernelOops
DistroRelease: Ubuntu 11.04
Package: linux-image-2.6.38-7-generic 2.6.38-7.39
Regression: Yes
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.38-7.39-generic 2.6.38
Uname: Linux 2.6.38-7-generic i686
NonfreeKernelModules: nvidia
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
Annotation: Your system might become unstable now and might need to be restarted.
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: shaman 1382 F.... pulseaudio
 /dev/snd/pcmC0D0p: shaman 1382 F...m pulseaudio
CRDA: Error: [Errno 2] Arquivo ou diretório não encontrado
Card0.Amixer.info:
 Card hw:0 'VT82xx'/'HDA VIA VT82xx at 0x9fffc000 irq 66'
   Mixer name : 'Realtek ALC883'
   Components : 'HDA:10ec0883,10438249,00100002'
   Controls : 38
   Simple ctrls : 21
Date: Mon Apr 4 09:54:51 2011
Failure: oops
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release i386 (20091028.5)
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.
MachineType: System manufacturer System Product Name
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-7-generic root=UUID=fee5ec12-b8a9-48e8-b12b-404d98a13139 ro splash vga=795 quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-2.6.38-7-generic N/A
 linux-backports-modules-2.6.38-7-generic N/A
 linux-firmware 1.49
RfKill:
 0: hci0: Bluetooth
  Soft blocked: no
  Hard blocked: no
SourcePackage: linux
Title: BUG: unable to handle kernel NULL pointer dereference at (null)
UpgradeStatus: Upgraded to natty on 2011-04-02 (2 days ago)
dmi.bios.date: 01/25/2007
dmi.bios.vendor: Phoenix Technologies, LTD
dmi.bios.version: ASUS P5VD2-X ACPI BIOS Revision 0304
dmi.board.name: P5VD2-X
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: 1.XX
dmi.chassis.asset.tag: 123456789000
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: 1111
dmi.modalias: dmi:bvnPhoenixTechnologies,LTD:bvrASUSP5VD2-XACPIBIOSRevision0304:bd01/25/2007:svnSystemmanufacturer:pnSystemProductName:pvr:rvnASUSTeKComputerINC.:rnP5VD2-X:rvr1.XX:cvnChassisManufacture:ct3:cvr1111:
dmi.product.name: System Product Name
dmi.sys.vendor: System manufacturer