CANT MOUNT MY 160gig SAMSUNG EXTERNAL HARD DRIVE IN UBUNTU, KEEPS GIVING ERROR

 The first time i installed ubuntu i was able to mount all my externals but it stoped working this morning. i cant mount it.
shows error: Error org.freedesktop.Hal.Device.UnknownError.

My system log
Sep 14 11:31:21 john-Pc dhclient: bound to 10.0.0.5 -- renewal in 1748 seconds.
Sep 14 11:31:24 john-Pc kernel: [10205.116267] usb 1-3: USB disconnect, address 5
Sep 14 11:31:25 john-Pc kernel: [10206.180165] usb 1-3: new high speed USB device using ehci_hcd and address 6
Sep 14 11:31:25 john-Pc kernel: [10206.316214] usb 1-3: configuration #1 chosen from 1 choice
Sep 14 11:31:26 john-Pc kernel: [10206.390532] scsi6 : SCSI emulation for USB Mass Storage devices
Sep 14 11:31:26 john-Pc kernel: [10206.392879] usb-storage: device found at 6
Sep 14 11:31:26 john-Pc kernel: [10206.392886] usb-storage: waiting for device to settle before scanning
Sep 14 11:31:31 john-Pc kernel: [10211.392364] usb-storage: device scan complete
Sep 14 11:31:31 john-Pc kernel: [10211.400718] scsi 6:0:0:0: Direct-Access SAMSUNG HD161HJ PQ: 0 ANSI: 2
Sep 14 11:31:31 john-Pc kernel: [10211.441659] sd 6:0:0:0: [sdb] 312581808 512-byte hardware sectors: (160 GB/149 GiB)
Sep 14 11:31:31 john-Pc kernel: [10211.450871] sd 6:0:0:0: [sdb] Write Protect is off
Sep 14 11:31:31 john-Pc kernel: [10211.450879] sd 6:0:0:0: [sdb] Mode Sense: 38 00 00 00
Sep 14 11:31:31 john-Pc kernel: [10211.450885] sd 6:0:0:0: [sdb] Assuming drive cache: write through
Sep 14 11:31:31 john-Pc kernel: [10211.452862] sd 6:0:0:0: [sdb] 312581808 512-byte hardware sectors: (160 GB/149 GiB)
Sep 14 11:31:31 john-Pc kernel: [10211.455994] sd 6:0:0:0: [sdb] Write Protect is off
Sep 14 11:31:31 john-Pc kernel: [10211.456001] sd 6:0:0:0: [sdb] Mode Sense: 38 00 00 00
Sep 14 11:31:31 john-Pc kernel: [10211.456027] sd 6:0:0:0: [sdb] Assuming drive cache: write through
Sep 14 11:31:34 john-Pc kernel: [10211.457126] sdb: sdb1
Sep 14 11:31:34 john-Pc kernel: [10215.172953] sd 6:0:0:0: [sdb] Attached SCSI disk
Sep 14 11:31:34 john-Pc kernel: [10215.173094] sd 6:0:0:0: Attached scsi generic sg2 type 0
Sep 14 11:37:51 john-Pc NetworkManager: <info> (wlan0): supplicant connection state: completed -> group handshake
Sep 14 11:37:51 john-Pc NetworkManager: <info> (wlan0): supplicant connection state: group handshake -> completed
Sep 14 11:40:01 john-Pc /USR/SBIN/CRON[13975]: (root) CMD ([ -x /usr/sbin/update-motd ] && /usr/sbin/update-motd 2>/dev/null)
Sep 14 11:50:01 john-Pc /USR/SBIN/CRON[14357]: (root) CMD ([ -x /usr/sbin/update-motd ] && /usr/sbin/update-motd 2>/dev/null)
Sep 14 11:50:02 john-Pc x-session-manager[10371]: WARNING: Client '/org/gnome/SessionManager/Client24' failed to reply before timeout
Sep 14 11:50:02 john-Pc x-session-manager[10371]: WARNING: Client '/org/gnome/SessionManager/Client9' failed to reply before timeout
Sep 14 11:50:02 john-Pc x-session-manager[10371]: WARNING: Client '/org/gnome/SessionManager/Client5' failed to reply before timeout
Sep 14 11:50:02 john-Pc x-session-manager[10371]: WARNING: Client '/org/gnome/SessionManager/Client2' failed to reply before timeout
Sep 14 11:50:12 john-Pc console-kit-daemon[2732]: GLib-GObject-WARNING: IA__g_object_get_valist: value location for `gchararray' passed as NULL
Sep 14 11:50:12 john-Pc last message repeated 12 times
Sep 14 11:50:12 john-Pc init: tty4 main process (2302) killed by TERM signal
Sep 14 11:50:12 john-Pc init: tty5 main process (2303) killed by TERM signal
Sep 14 11:50:12 john-Pc init: tty2 main process (2309) killed by TERM signal
Sep 14 11:50:12 john-Pc init: tty3 main process (2311) killed by TERM signal
Sep 14 11:50:12 john-Pc init: tty6 main process (2312) killed by TERM signal
Sep 14 11:50:12 john-Pc init: tty1 main process (3308) killed by TERM signal
Sep 14 11:50:12 john-Pc console-kit-daemon[2732]: GLib-GObject-WARNING: IA__g_object_get_valist: value location for `gchararray' passed as NULL
Sep 14 11:50:13 john-Pc last message repeated 3 times

Pls, kindly tell me how to fix this...pls pls pls