Like many here, I had the same problem when upgrading natty server to oneiric server. The conversion/migration of /var/run to /run during the upgrade process is buggy causing all sorts of problems until the content of /var/run and /var/lock are moved to /run and symlinks are created shown below as per comment #18.
ls -l /var/run /var/lock
lrwxrwxrwx 1 root root 9 2011-10-23 12:24 /var/lock -> /run/lock/
lrwxrwxrwx 1 root root 4 2011-10-23 12:23 /var/run -> /run/
PS: The strange thing is, I upgraded my desktop version last week from natty->oneiric, the upgrade went just fine with the migration done properly.