I have updated natty too and problem does not disappeared. It is not fixed.

dmesg output:

Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605901] radeon 0000:01:00.0: GPU lockup CP stall for more than 10000msec
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605909] ------------[ cut here ]------------
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605978] WARNING: at /build/buildd/linux-2.6.38/drivers/gpu/drm/radeon/radeon_fence.c:248 radeon_fence_wait+0x36f/0x3e0 [radeon]()
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605980] Hardware name: HP EliteBook 8460p
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605981] GPU lockup (waiting for 0x00098B58 last fence id 0x00098B55)
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.605982] Modules linked in: snd_seq_dummy nls_utf8 udf aesni_intel cryptd aes_x86_64 aes_generic binfmt_misc rfcomm sco bnep l2cap kvm_intel kvm nls_iso8859_1 nls_cp437 vfat fat dm_crypt ip6t_LOG xt_hl ip6t_rt nf_conntrack_ipv6 nf_defrag_ipv6 ipt_REJECT xt_recent xt_comment ipt_LOG xt_limit xt_multiport snd_hda_codec_hdmi xt_tcpudp snd_hda_codec_idt ipt_addrtype snd_hda_intel xt_state snd_hda_codec snd_hwdep snd_pcm ip6table_filter ip6_tables snd_seq_midi snd_rawmidi nf_nat_irc nf_conntrack_irc tpm_infineon arc4 nf_nat_ftp nf_nat snd_seq_midi_event max6650 nf_conntrack_ipv4 snd_seq joydev nf_defrag_ipv4 tpm_tis ppdev tpm coretemp nf_conntrack_ftp nf_conntrack iwlagn iwlcore uvcvideo snd_timer snd_seq_device parport_pc psmouse tpm_bios hp_accel lp hp_wmi btusb lis3lv02d input_polldev serio_raw snd videodev sparse_keymap v4l2_compat_ioctl32 iptable_filter soundcore ip_tables x_tables mac80211 bluetooth snd_page_alloc cfg80211 parport usbhid hid radeon ahci libahci sdhci_pci fir
Jul 28 11:51:04 Pali-EliteBook kernel: ewire_ohci ttm e1000e drm_kms_helper sdhci drm xhci_hcd firewire_core crc_itu_t i2c_algo_bit video
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606021] Pid: 2433, comm: SC2.exe Tainted: G        W   2.6.38-11-generic #47-Ubuntu
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606022] Call Trace:
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606027]  [<ffffffff81065cbf>] ? warn_slowpath_common+0x7f/0xc0
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606029]  [<ffffffff81065db6>] ? warn_slowpath_fmt+0x46/0x50
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606038]  [<ffffffffa01537cf>] ? radeon_fence_wait+0x36f/0x3e0 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606042]  [<ffffffff81087fb0>] ? autoremove_wake_function+0x0/0x40
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606050]  [<ffffffffa01540b1>] ? radeon_sync_obj_wait+0x11/0x20 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606055]  [<ffffffffa010fb0d>] ? ttm_bo_wait+0xfd/0x1b0 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606060]  [<ffffffffa01127e6>] ? ttm_bo_move_accel_cleanup+0x1c6/0x260 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606068]  [<ffffffffa015436f>] ? radeon_move_blit.clone.0+0x11f/0x180 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606075]  [<ffffffffa0154685>] ? radeon_move_ram_vram.clone.2+0x125/0x150 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606078]  [<ffffffff81124517>] ? vma_prio_tree_next+0x47/0x70
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606082]  [<ffffffffa01153db>] ? ttm_eu_list_ref_sub+0x3b/0x60 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606089]  [<ffffffffa0154898>] ? radeon_bo_move+0x1e8/0x1f0 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606094]  [<ffffffffa011089e>] ? ttm_bo_handle_move_mem+0x12e/0x3d0 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606098]  [<ffffffffa0111982>] ? ttm_bo_move_buffer+0x142/0x160 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606102]  [<ffffffffa01153db>] ? ttm_eu_list_ref_sub+0x3b/0x60 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606106]  [<ffffffffa0111a36>] ? ttm_bo_validate+0x96/0x120 [ttm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606114]  [<ffffffffa015583c>] ? radeon_bo_list_validate+0x7c/0xe0 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606124]  [<ffffffffa016e6c6>] ? radeon_cs_parser_relocs+0x236/0x270 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606133]  [<ffffffffa016eb51>] ? radeon_cs_ioctl+0xa1/0x1e0 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606141]  [<ffffffffa004f384>] ? drm_ioctl+0x3e4/0x4c0 [drm]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606150]  [<ffffffffa016eab0>] ? radeon_cs_ioctl+0x0/0x1e0 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606152]  [<ffffffff815c71b8>] ? do_page_fault+0x258/0x540
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606162]  [<ffffffffa01ce4d4>] ? radeon_kms_compat_ioctl+0x14/0x30 [radeon]
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606164]  [<ffffffff811b0231>] ? compat_sys_ioctl+0xe1/0x360
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606167]  [<ffffffff81092dfa>] ? do_gettimeofday+0x1a/0x50
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606169]  [<ffffffff810486c0>] ? sysenter_dispatch+0x7/0x2e
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.606170] ---[ end trace eb7d1b915da7c315 ]---
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607312] radeon 0000:01:00.0: GPU softreset 
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607314] radeon 0000:01:00.0:   GRBM_STATUS=0xB2733828
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607316] radeon 0000:01:00.0:   GRBM_STATUS_SE0=0x1C000007
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607318] radeon 0000:01:00.0:   GRBM_STATUS_SE1=0x00000007
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607320] radeon 0000:01:00.0:   SRBM_STATUS=0x200000C0
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607374] radeon 0000:01:00.0:   GRBM_SOFT_RESET=0x00007F6B
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607479] radeon 0000:01:00.0:   GRBM_STATUS=0x00003828
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607482] radeon 0000:01:00.0:   GRBM_STATUS_SE0=0x00000007
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607485] radeon 0000:01:00.0:   GRBM_STATUS_SE1=0x00000007
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.607488] radeon 0000:01:00.0:   SRBM_STATUS=0x200000C0
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.608489] radeon 0000:01:00.0: GPU reset succeed
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.630153] radeon 0000:01:00.0: WB enabled
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.646538] [drm] ring test succeeded in 2 usecs
Jul 28 11:51:04 Pali-EliteBook kernel: [ 9658.646553] [drm] ib test succeeded in 3 usecs