OfficeJet Pro 8500 A910a not printing duplex

In the system dialog, I am not given the option of printing double-sided.

In the HP Device Manager settings, I have it set at "Two sided (long edge)"

Does not print double sided.

HP Linux Imaging and Printing System (ver. 3.13.2)
Dependency/Version Check Utility ver. 15.1

Copyright (c) 2001-13 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Note: hp-check can be run in three modes:
1. Compile-time check mode (-c or --compile): Use this mode before compiling the
HPLIP supplied tarball (.tar.gz or .run) to determine if the proper dependencies
are installed to successfully compile HPLIP.
2. Run-time check mode (-r or --run): Use this mode to determine if a distro
supplied package (.deb, .rpm, etc) or an already built HPLIP supplied tarball
has the proper dependencies installed to successfully run.
3. Both compile- and run-time check mode (-b or --both) (Default): This mode
will check both of the above cases (both compile- and run-time dependencies).

Check types:
a. EXTERNALDEP - External Dependencies
b. GENERALDEP - General Dependencies (required both at compile and run time)
c. COMPILEDEP - Compile time Dependencies
d. [All are run-time checks]
PYEXT SCANCONF QUEUES PERMISSION

Status Types:
    OK
    MISSING - Missing Dependency or Permission or Plug-in
    INCOMPAT - Incompatible dependency-version or Plugin-version

warning: debian-6.0.7 version is not supported. Using debian-6.0.6 versions dependencies to verify and install...

---------------
| SYSTEM INFO |
---------------

 Kernel: 2.6.32-5-amd64 #1 SMP Mon Feb 25 00:26:11 UTC 2013 GNU/Linux
 Host: beast
 Proc: 2.6.32-5-amd64 #1 SMP Mon Feb 25 00:26:11 UTC 2013 GNU/Linux
 Distribution: debian 6.0.7

-----------------------
| HPLIP CONFIGURATION |
-----------------------

HPLIP-Version: HPLIP 3.13.2
HPLIP-Home: /usr/share/hplip
warning: HPLIP-Installation: Auto installation is not supported for debian distro 6.0.7 version

Current contents of '/etc/hp/hplip.conf' file:
# hplip.conf. Generated from hplip.conf.in by configure.

[hplip]
version=3.13.2

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/HP
ppdbase=/usr/share/ppd
doc=/usr/share/doc/hplip-3.13.2
icon=/usr/share/applications
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv/hp
bin=/usr/bin

# Following values are determined at configure time and cannot be changed.
[configure]
network-build=yes
libusb01-build=no
pp-build=no
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=no
foomatic-drv-install=no
foomatic-ppd-install=no
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.13.2
restricted-build=no
ui-toolkit=qt4
qt3=no
qt4=yes
policy-kit=no
hpijs-only-build=no
lite-build=no
udev-acl-rules=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no

Current contents of '/var/lib/hp/hplip.state' file:
Plugins are not installed. Could not access file: No such file or directory

Current contents of '~/.hplip/hplip.conf' file:
[last_used]
printer_name =
working_dir = .
device_uri = "hp:/net/Officejet_Pro_8500_A910?zc=HP60A515"

[commands]
scan = /usr/bin/xsane -V %SANE_URI%

[upgrade]
notify_upgrade = true
last_upgraded_time = 1362707964
pending_upgrade_time = 0

[installation]
date_time = 03/07/2013 20:17:53
version = 3.13.2

[settings]
systray_messages = 0
systray_visible = 0

[fax]
email_address =
voice_phone =

[refresh]
rate = 30
enable = false
type = 1

[polling]
enable = false
device_list =
interval = 5

 <Package-name> <Package-Desc> <Required/Optional> <Min-Version> <Installed-Version> <Status> <Comment>

--------------------------
| External Dependencies |
--------------------------

 gs Ghostscript REQUIRED 7.05 8.71 OK -
 network Network-wget OPTIONAL - 1.12 OK -
 dbus DBus REQUIRED - 1.2.24 OK -
 scanimage Shell-Scanning OPTIONAL 1.0 1.0.21 OK -
 policykit Admin-Policy-framework OPTIONAL - 0.96 OK -
 xsane SANE-GUI OPTIONAL 0.9 0.997 OK -
 cups CUPS REQUIRED 1.1 1.4.4 OK 'CUPS Scheduler is running'

-------------------------
| General Dependencies |
-------------------------

 reportlab Python-PDF-Lib OPTIONAL 2.0 2.4 OK -
 libcrypto OpenSSL-Crypto-Lib REQUIRED - 0.9.8 OK -
 pil Python-Image-Lib OPTIONAL - 1.1.7 OK -
 pyqt4-dbus PyQt4-DBUS REQUIRED 4.0 4.7.3 OK -
 libjpeg JPEG-Lib REQUIRED - - OK -
 libpthread POSIX-Threads-Lib REQUIRED - 2.11.3 OK -
 python-dbus Python-DBUS REQUIRED 0.80.0 0.83.1 OK -
 python-devel Python-SDK REQUIRED 2.2 2.6.6 OK -
 pyqt4 Python-Qt4 REQUIRED 4.0 4.7.3 OK -
 cups-devel CUPS-SDK REQUIRED - 1.4.4 OK -
 sane-devel SANE-SDK REQUIRED - 1.0.21 OK -
 libusb USB-Lib REQUIRED - 1.0 OK -
 sane Scan-Lib REQUIRED - 1.0.21 OK -
 cups-image CUPS-Image-Lib REQUIRED - 1.4.4 OK -
 libnetsnmp-devel SNMP-Networking-SDK REQUIRED 5.0.9 5.4.3 OK -
 python-xml Python-XML-Lib REQUIRED - 2.1.0 OK -
 python-notify Desktop-notifications OPTIONAL - - OK -

------------------------------
| Compile Time Dependencies |
------------------------------

 gcc gcc-Compiler REQUIRED - 4.4.5 OK -
 libtool Build-tools REQUIRED - 2.2.6 OK -
 make GNU-Build-tools REQUIRED 3.0 3.81 OK -

----------------------
| Python Extentions |
----------------------

 cupsext CUPS-Extension REQUIRED - 3.13.2 OK -
 pcardext PhotoCard-Extension REQUIRED - 3.13.2 OK -
 hpmudext IO-Extension REQUIRED - 3.13.2 OK -

-----------------------
| Scan Configuration |
-----------------------

 hpaio HPLIP-SANE-Backend REQUIRED - 3.13.2 OK 'hpaio found in /etc/sane.d/dll.conf'
 scanext Scan-SANE-Extension REQUIRED - 3.13.2 OK -

------------------------------
| DISCOVERED SCANNER DEVICES |
------------------------------

device `hpaio:/net/Officejet_Pro_8500_A910?zc=HP60A515' is a Hewlett-Packard Officejet_Pro_8500_A910 all-in-one
device `v4l:/dev/video0' is a Noname CNF8215 virtual device

--------------------------
| DISCOVERED USB DEVICES |
--------------------------

No devices found.

---------------------------------
| INSTALLED CUPS PRINTER QUEUES |
---------------------------------

Officejet_Pro_8500_A910
-----------------------
Type: Printer
Device URI: hp:/net/Officejet_Pro_8500_A910?zc=HP60A515
PPD: /etc/cups/ppd/Officejet_Pro_8500_A910.ppd
PPD Description: HP Officejet Pro 8500 a910, hpcups 3.13.2
Printer status: printer Officejet_Pro_8500_A910 is idle. enabled since Thu 07 Mar 2013 ready to printT
Communication status: Good

Officejet_Pro_8500_A910_fax
---------------------------
Type: Fax
Device URI: hpfax:/net/Officejet_Pro_8500_A910?zc=HP60A515
PPD: /etc/cups/ppd/Officejet_Pro_8500_A910_fax.ppd
PPD Description: HP Fax4 hpcups
Printer status: printer Officejet_Pro_8500_A910_fax is idle. enabled since Thu 07 Mar 2013 08:00:19 PM CST
Communication status: Good

--------------
| PERMISSION |
--------------

groups user-groups Required - - OK dols adm lp cdrom floppy audio dip video plugdev staff netdev bluetooth lpadmin fuse scanner

libusb couldn't open USB device /dev/bus/usb/002/043: Permission denied.
libusb requires write access to USB device nodes.
warning: Device URI: (Makeuri FAILED)
libusb couldn't open USB device /dev/bus/usb/002/040: Permission denied.
libusb requires write access to USB device nodes.
warning: Device URI: (Makeuri FAILED)
No errors or warnings.

Done.