Comment 58 for bug 127101

I do not know if anyone knows of this but have you tried the following:

for Ubuntu:

Type in a terminal :

sudo gdmsetup -> In the general tab tick the "Restart the X server with each login"

for Kubuntu:

you've got to add or uncomment the line

TerminateServer=true

in the [X-:*-Core] section of the kdmrc-File (/etc/kde3/kdm/kdmrc) - beware of the ':', there is a similar named section without it, too!

Seems to work for many.