I have just installed the new linux-image-2.6.32-25 from Ubuntu repositories, and faced this problem too.
The booting stops just before KDM screen should appear after the KUbuntu logo
Xorg.0.log contained the same lines:
Fatal server error:
xf86OpenConsole: VT_WAITACTIVE failed: Interrupted system call
I could not boot my computer three times concequently, including the "failsafeX" mode. I could load it only without any graphical login manager, and used this opportunity to reinstall back 2.6.32-24 kernel. However, after that the 2.6.32-25 kernel is booting normally. Not sure how this could be reproduced again.
I've never seen such things with earlier kernels.