Comment 3 for bug 875402

I had the same problem, it looks like pexec is no more working on recent Ubuntu version.
It was generating a lot of crash windows at startup.

A quick and dirty fix (no more errors at least):
# sudo mv /usr/bin/pkexec /usr/bin/pkexec.old
# sudo ln -s /usr/bin/gksudo /usr/bin/pkexec

Sincerely

Technical Details:

ProblemType: Crash
Architecture: amd64
CrashCounter: 1
Date: Sat Nov 9 14:35:29 2013
DistroRelease: Ubuntu 13.10
ExecutablePath: /usr/bin/pkexec
ExecutableTimestamp: 1379527177
ProcCmdline: pkexec /usr/lib/update-notifier/package-system-locked
ProcCwd: /home/mystercoco
ProcEnviron:
 TERM=xterm
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=fr_FR.UTF-8
 LANGUAGE=fr_FR
 XDG_RUNTIME_DIR=<set>