I set up a CUPS server with a few queues and printing from local clients (the CUPS test page and Samba) seems to work just fine.

It seems like the CUPS server is denying non-local clients though:

130.127.48.70 - - [03/Jun/2014:14:29:19 -0400] "POST /printers/m137 HTTP/1.1" 200 390 Validate-Job successful-ok
130.127.48.70 - - [03/Jun/2014:14:29:19 -0400] "POST /printers/m137 HTTP/1.1" 200 339 Create-Job client-error-not-authorized
localhost - - [03/Jun/2014:14:40:50 -0400] "POST /printers/m137 HTTP/1.1" 200 410869 Print-Job successful-ok

This makes me think I have some sort of host-based restriction in my configuration file, but I can't find it. I've even set my default policy to Allow all only to get the same log message. I'm working from a configuration file which had previously worked on an older version of CUPS, which looks quite similar to the example cupsd.conf. I could be wrong but it looks like that final <Limit All> block ought to allow the actions the logs complain about.

MaxLogSize 2000000000

# Log general information in error_log - change "info" to "debug" for
# troubleshooting...
LogLevel info
#AccessLog syslog
#ErrorLog syslog
#PageLog syslog

# Administrator user group...
SystemGroup sys root lp

# Only listen for connections from the local machine.
Listen 0.0.0.0:631
Listen :::631
Listen /var/run/cups/cups.sock

ServerName <snipped>

# Show shared printers on the local network.
Browsing Off
BrowseOrder allow,deny
# (Change '@LOCAL' to 'ALL' if using directed broadcasts from another subnet.)
BrowseAllow @LOCAL

# Default authentication type, when authentication is required...
DefaultAuthType Basic

# Restrict access to the server...
<Location />
  Order allow,deny
  Allow all
</Location>

# Restrict access to the admin pages...
<Location /admin>
  AuthType Default
  Require user @SYSTEM
  Encryption Required
  Order allow,deny
  Allow all
</Location>

# Restrict access to configuration files...
<Location /admin/conf>
  AuthType Default
  Require user @SYSTEM
  Encryption Required
  Order allow,deny
  Allow all
</Location>

# Set the default printer/job policies...
<Policy default>  
  # Job-related operations must be done by the owner or an administrator...
  <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 CUPS-Move-Job>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </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>
    AuthType Default
    Require user @SYSTEM
    Order deny,allow
  </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 CUPS-Accept-Jobs CUPS-Reject-Jobs>
    AuthType Default
    Require user @SYSTEM
    Order deny,allow
  </Limit>

  # Only the owner or an administrator can cancel or authenticate a job...
  <Limit Cancel-Job CUPS-Authenticate-Job>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </Limit>

  <Limit All>
    Order allow,deny
  </Limit>
</Policy>