Hello. I'm running a fully updated natty but still experiencing this bug.

Jul  4 16:12:59 psaraiva-ubuntu kernel: [23743.951151] npviewer.bin[8714]: segfault at f2218af8 ip 00000000f7061bc8 sp 00000000f09fe04c error 6 in libpthread-2.13.so[f7057000+15000]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969721] radeon 0000:01:00.0: GPU lockup CP stall for more than 608400msec
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969726] ------------[ cut here ]------------
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969753] WARNING: at /build/buildd/linux-2.6.38/drivers/gpu/drm/radeon/radeon_fence.c:248 radeon_fence_wait+0x36f/0x3e0 [radeon]()
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969758] Hardware name: System Product Name
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969761] GPU lockup (waiting for 0x01C8C927 last fence id 0x01C8C917)
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969764] Modules linked in: binfmt_misc parport_pc ppdev snd_hda_codec_hdmi snd_hda_codec_via snd_hda_intel radeon snd_hda_codec snd_hwdep snd_pcm ttm snd_seq_midi drm_kms_helper snd_rawmidi joydev snd_seq_midi_event snd_seq psmouse snd_timer snd_seq_device drm i2c_algo_bit snd soundcore serio_raw snd_page_alloc asus_atk0110 lp parport usbhid hid pata_via r8169
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969802] Pid: 921, comm: Xorg Not tainted 2.6.38-8-generic #42-Ubuntu
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969805] Call Trace:
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969814]  [<ffffffff81065cef>] ? warn_slowpath_common+0x7f/0xc0
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969820]  [<ffffffff81065de6>] ? warn_slowpath_fmt+0x46/0x50
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969843]  [<ffffffffa01cd6df>] ? radeon_fence_wait+0x36f/0x3e0 [radeon]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969850]  [<ffffffff81087f30>] ? autoremove_wake_function+0x0/0x40
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969873]  [<ffffffffa01cdfc1>] ? radeon_sync_obj_wait+0x11/0x20 [radeon]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969882]  [<ffffffffa013fb0d>] ? ttm_bo_wait+0xfd/0x1b0 [ttm]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969891]  [<ffffffffa013fe88>] ? ttm_bo_list_ref_sub+0x28/0x30 [ttm]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969917]  [<ffffffffa01e69e3>] ? radeon_gem_wait_idle_ioctl+0x93/0x110 [radeon]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969931]  [<ffffffffa0097384>] ? drm_ioctl+0x3e4/0x4c0 [drm]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969957]  [<ffffffffa01e6950>] ? radeon_gem_wait_idle_ioctl+0x0/0x110 [radeon]
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969964]  [<ffffffff81010f0e>] ? arch_get_unmapped_area_topdown+0x1ce/0x2f0
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969972]  [<ffffffff8117648f>] ? do_vfs_ioctl+0x8f/0x360
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969977]  [<ffffffff811767f1>] ? sys_ioctl+0x91/0xa0
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969983]  [<ffffffff8100c002>] ? system_call_fastpath+0x16/0x1b
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969987] ---[ end trace 9ee964e113de671b ]---
Jul  4 17:44:01 psaraiva-ubuntu kernel: [29198.969999] [drm] Disabling audio support