I have this problem. Nvidia left of work suddenly with driver:
With and x86signanling cautch error. After some probes (recompiling driver, a lof of times, using experimental packages from X) I discover and error in libglx.so. So I remove nvidia drivers, and X runs prefect.
I discover this post, and apply the fix form the bugs list in debian:
Reinstalled the drivers, and no nvidia works again. Definitively there is a problem with nvidia drivers and noexec in UDEV.
ii udev 0.113-2 /dev/ and hotplug management daemon
Thanks for reporting I was crying without my twinview.