Talvez você já tenha corrigido isso, mas eu tive o mesmo problema. Resolveu-o alterando "Ordenar negar, permitir" para "Encomendar permitir, negar" e remover todas as coisas de Autenticação.
Este é o meu arquivo de configuração:
#
# Configuration file for the CUPS scheduler. See "man cupsd.conf" for a
# complete description of this file.
#
# Log general information in error_log - change "warn" to "debug"
# for troubleshooting...
LogLevel warn
PageLogFormat
# Deactivate CUPS' internal logrotating, as we provide a better one, especially
# LogLevel debug2 gets usable now
MaxLogSize 0
# Only listen for connections from the local machine.
Listen 631
Listen /var/run/cups/cups.sock
# Show shared printers on the local network.
Browsing Off
BrowseLocalProtocols dnssd
# Default authentication type, when authentication is required...
DefaultAuthType None
# Web interface setting...
WebInterface Yes
# Restrict access to the server...
<Location />
Order allow,deny
Allow all
</Location>
# Restrict access to the admin pages...
<Location /admin>
Order allow,deny
Allow all
</Location>
# Restrict access to configuration files...
<Location /admin/conf>
AuthType None
Order allow,deny
</Location>
# Restrict access to log files...
<Location /admin/log>
AuthType None
Order allow,deny
</Location>
# Set the default printer/job policies...
<Policy default>
# Job/subscription privacy...
JobPrivateAccess default
JobPrivateValues default
SubscriptionPrivateAccess default
SubscriptionPrivateValues default
# Job-related operations must be done by the owner or an administrator...
<Limit Create-Job Print-Job Print-URI Validate-Job>
Order deny,allow
</Limit>
<Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document>
#Require user @OWNER @SYSTEM
#Order deny,allow
Order allow,deny
</Limit>
# All administration operations require an administrator to authenticate...
<Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default CUPS-Get-Devices>
AuthType None
Order allow,deny
</Limit>
# All printer operations require a printer operator to authenticate...
<Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs>
Order allow,deny
</Limit>
# Only the owner or an administrator can cancel or authenticate a job...
<Limit Cancel-Job CUPS-Authenticate-Job>
Order allow,deny
</Limit>
<Limit All>
Order allow,deny
</Limit>
</Policy>
# Set the authenticated printer/job policies...
<Policy authenticated>
# Job/subscription privacy...
JobPrivateAccess default
JobPrivateValues default
SubscriptionPrivateAccess default
SubscriptionPrivateValues default
# Job-related operations must be done by the owner or an administrator...
<Limit Create-Job Print-Job Print-URI Validate-Job>
Order allow,deny
</Limit>
<Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document>
Order allow,deny
</Limit>
# All administration operations require an administrator to authenticate...
<Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default>
Order allow,deny
</Limit>
# All printer operations require a printer operator to authenticate...
<Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs>
Order allow,deny
</Limit>
# Only the owner or an administrator can cancel or authenticate a job...
<Limit Cancel-Job CUPS-Authenticate-Job>
Order allow,deny
</Limit>
<Limit All>
Order allow,deny
</Limit>
</Policy>