Desktop effects don't work

[AlbertH]

Binary package hint: kdebase-workspace

After I installed kubuntu 10.10 beta, desktop effects don't work any more.
They are disabled on login, it's not possible to enable them in systemsettigs and no explanations about failure are given.
Effects work without problem in kubuntu Lucid.
If you need more information about my hardware, please ask, I will be happy to help.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: kde-window-manager 4:4.5.0b-0ubuntu6
ProcVersionSignature: Ubuntu 2.6.35-19.28-generic 2.6.35.3
Uname: Linux 2.6.35-19-generic i686
Architecture: i386
Date: Fri Sep 3 01:57:51 2010
InstallationMedia: Kubuntu 10.10 "Maverick Meerkat" - Beta i386 (20100902.1)
ProcEnviron:
 LANGUAGE=it_IT
 LANG=it_IT.utf8
 SHELL=/bin/bash
SourcePackage: kdebase-workspace