Comment 13 for bug 441653

Same bug here: on Lucid (Ubuntu, not Kubuntu) with Xorg radeon driver and an older ATI Radeon 9250 card with two monitors in clone mode: it happened two times to me since upgrade from Hardy to Lucid, and every time the computer hung on boot but I was able to reboot with C-A-D.

/var/log/Xorg.1.log.old says:
Fatal server error:
xf86OpenConsole: VT_WAITACTIVE failed: Interrupted system call
...
 ddxSigGiveUp: Closing log

So summarizing:
This happens with ATI cards with Xorg and fglrx drivers, with Nvidia and with Intel cards and even within VMware, so it has nothing to do with the driver, but it has something to do with the X-server.