Solved with the new version or with the following modification to the xorg.conf. Don't know which one since I do both at the same time :-(
Section "Extensions" Option "Composite" "Disable" EndSection -- Xlib: extension "GLX" missing on display ":0.0" https://launchpad.net/bugs/63461 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs