It happened me with a few different setups that suddenly, after an update, all printers disappeared from the printing dialog.
The smart would then check if cups is running with

sudo /etc/init.d/smart status

but would see a [failed] output.

The dmesg log would prompt you with some messages like the following one:

operation="sysctl" requested_mask="r::" denied_mask="r::" fsuid=0 name="/proc/sys/crypto/fips_enabled" pid=NNNNN profile="/usr/sbin/cupsd"

In short this is a bug of apparmor fixed in version 2.3.1+1403-0ubuntu7 in karmic. The fix basically consist in adding a missing line

@{PROC} /sys/crypto/fips_enabled r,

to file /etc/apparmor.d/usr.sbin.cupsd

where you see others @{PROC} lines

reloading apparmor is achieved by

sudo /etc/init.d/apparmor reload

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