After logout from user account greeter is not displayed

[yesint]

After usual update I got the following problem:
I have 3 users - one with sudo priviledges and 2 ordinary. When ordinary user logs out the black screen is shown - no greeter, just nothing. Doing "sudo stop lightdm; sudo start lightdm" doesn't help - the same black screen. Only restart helps.
There is no such problem with sudo user - log out works just fine for it and greeter is shown.
I have no idea how to locate the problem.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xorg 1:7.6+12ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-26.41-generic 3.2.19
Uname: Linux 3.2.0-26-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu11
Architecture: amd64
Date: Sun Jul 29 09:32:42 2012
InstallationMedia: Xubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
SourcePackage: xorg
Symptom: display
UpgradeStatus: No upgrade log present (probably fresh install)