Comment 21 for bug 441653

I do have the same problem on my HP Compaq 615 (graphics card: AMD HD 3200). It only happens when the fglrx drivers are installed, which results in KMS being disabled. It does *not* matter whether I have an xorg.conf file to tell X to actually use the fglrx driver. This is the Xorg.0.log error message:
Fatal server error:
xf86OpenConsole: VT_WAITACTIVE failed: Interrupted system call

When above conditions are met, the lockup occurs about every 3rd to 4th time. Ctrl+Alt+Del sanely restarts the machine.
While googling for the problem, I found this old issue in Red Had with exactly the same symptoms (as in, only happening with KDM, irreproducible, and same error in X log file):