Similar issue here. I'm fairly sure I saw different errors, i.e. not only nvidia.

After the below example, it's dead. It always concerns IRQ's. I enclose some examples from a rich gallery I have in /var/log.

 name [ 1377.796013] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 name [ 1377.796088] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 name [ 1377.796013] NVRM: os_pci_init_handle: invalid context!
 name last message repeated 4 times
 name [ 1380.200095] irq 16: nobody cared (try booting with the "irqpo
ll" option)
 name [ 1380.200102] Pid: 3019, comm: mplayer Tainted: P O 3
.2.0-35-generic #55-Ubuntu
 name [ 1380.200105] Call Trace:
 name [ 1380.200113] [<c1560f2c>] ? printk+0x2d/0x2f
 name [ 1380.200119] [<c10b1259>] __report_bad_irq+0x29/0xd0
 name [ 1380.200123] [<c10b14b4>] note_interrupt+0x104/0x150
 name [ 1380.200127] [<c10af38f>] handle_irq_event_percpu+0x9f/0x1f0
 name [ 1380.200132] [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 name [ 1380.200136] [<c157614d>] ? _raw_spin_lock_irqsave+0x2d/0x40
 name [ 1380.200140] [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 name [ 1380.200144] [<c101e56d>] ? __io_apic_modify_irq+0x7d/0x90
 name [ 1380.200148] [<c10af51b>] handle_irq_event+0x3b/0x60
 name [ 1380.200152] [<c10b1cc0>] ? unmask_irq+0x30/0x30
 name [ 1380.200156] [<c10b1d0e>] handle_fasteoi_irq+0x4e/0xd0
 name [ 1380.200158] <IRQ> [<c157d832>] ? do_IRQ+0x42/0xc0
 name [ 1380.200165] [<c157d770>] ? common_interrupt+0x30/0x38
 name [ 1380.200169] [<c1570000>] ? add_i2c_device+0x126/0x166
 name [ 1380.200172] handlers:
 name [ 1380.200281] [<f9833050>] nv_kern_isr
 name [ 1380.200284] Disabling IRQ #16

 [12639.702668] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 [12639.702675] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 [12639.702693] NVRM: os_pci_init_handle: invalid context!
 [12639.702697] NVRM: os_pci_init_handle: invalid context!
 [12639.702750] NVRM: os_pci_init_handle: invalid context!
 [12639.702764] NVRM: os_pci_init_handle: invalid context!
 [12639.702768] NVRM: os_pci_init_handle: invalid context!
 [12641.590004] irq 16: nobody cared (try booting with the "irqpo
ll" option)
 [12641.590010] Pid: 1332, comm: Xorg Tainted: P           O 3.2.
0-35-generic #55-Ubuntu
 [12641.590013] Call Trace:
 [12641.590022]  [<c1560f2c>] ? printk+0x2d/0x2f
 [12641.590028]  [<c10b1259>] __report_bad_irq+0x29/0xd0
 [12641.590032]  [<c10b14b4>] note_interrupt+0x104/0x150
 [12641.590036]  [<c10af38f>] handle_irq_event_percpu+0x9f/0x1f0
 [12641.590041]  [<c10b1d90>] ? handle_fasteoi_irq+0xd0/0xd0
 [12641.590045]  [<c15776f1>] ? do_nmi+0x61/0x80
 [12641.590050]  [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 [12641.590054]  [<c101e56d>] ? __io_apic_modify_irq+0x7d/0x90
 [12641.590058]  [<c10af51b>] handle_irq_event+0x3b/0x60
 [12641.590041]  [<c10b1d90>] ? handle_fasteoi_irq+0xd0/0xd0
 [12641.590045]  [<c15776f1>] ? do_nmi+0x61/0x80
 [12641.590050]  [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 [12641.590054]  [<c101e56d>] ? __io_apic_modify_irq+0x7d/0x90
 [12641.590058]  [<c10af51b>] handle_irq_event+0x3b/0x60
 [12641.590061]  [<c10b1cc0>] ? unmask_irq+0x30/0x30
 [12641.590065]  [<c10b1d0e>] handle_fasteoi_irq+0x4e/0xd0
 [12641.590067]  <IRQ>  [<c157d832>] ? do_IRQ+0x42/0xc0
 [12641.590074]  [<c1002de3>] ? sys_sigreturn+0x93/0xa0
 [12641.590078]  [<c157d770>] ? common_interrupt+0x30/0x38
 [12641.590081] handlers:
 [12641.590189] [<f95bb050>] nv_kern_isr
 [12641.590192] Disabling IRQ #16

 [19994.912076] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 [19994.912079] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
 [19994.912095] NVRM: os_pci_init_handle: invalid context!
 [19994.912098] NVRM: os_pci_init_handle: invalid context!
 [19994.912148] NVRM: os_pci_init_handle: invalid context!
 [19994.912159] NVRM: os_pci_init_handle: invalid context!
 [19994.912161] NVRM: os_pci_init_handle: invalid context!
 [19997.209478] irq 16: nobody cared (try booting with the "irqpo
ll" option)
 [19997.209485] Pid: 7751, comm: kwin Tainted: P           O 3.2.0-35-generic #55-Ubuntu
 [19997.209488] Call Trace:
 [19997.209496]  [<c1560f2c>] ? printk+0x2d/0x2f
 [19997.209503]  [<c10b1259>] __report_bad_irq+0x29/0xd0
 [19997.209507]  [<c10b14b4>] note_interrupt+0x104/0x150
 [19997.209512]  [<c10249c3>] ? read_hpet+0x13/0x20
 [19997.209516]  [<c10af38f>] handle_irq_event_percpu+0x9f/0x1f0
 [19997.209520]  [<c10b1d90>] ? handle_fasteoi_irq+0xd0/0xd0
 [19997.209525]  [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 [19997.209529]  [<c157614d>] ? _raw_spin_lock_irqsave+0x2d/0x40
 [19997.209533]  [<c10af51b>] handle_irq_event+0x3b/0x60
 [19997.209536]  [<c10b1cc0>] ? unmask_irq+0x30/0x30
 [19997.209540]  [<c10b1d0e>] handle_fasteoi_irq+0x4e/0xd0
 [19997.209542]  <IRQ>  [<c157d832>] ? do_IRQ+0x42/0xc0
 [19997.209550]  [<c103a198>] ? pick_next_task_fair+0x48/0x50
 [19997.209554]  [<c157d770>] ? common_interrupt+0x30/0x38
 [19997.209558]  [<c10249c3>] ? read_hpet+0x13/0x20
 [19997.209563]  [<c1074597>] ? ktime_get_ts+0x67/0x120
 [19997.209567]  [<c106860f>] ? posix_ktime_get_ts+0xf/0x20
 [19997.209571]  [<c1069544>] ? sys_clock_gettime+0x24/0x70
 [19997.209574]  [<c15762f4>] ? syscall_call+0x7/0xb
 [19997.209579]  [<c1570000>] ? add_i2c_device+0x126/0x166
 [19997.209581] handlers:
 [19997.209694] [<f94f3050>] nv_kern_isr
 [19997.209697] Disabling IRQ #16


 [ 4750.600194] Pid: 0, comm: swapper/0 Tainted: P           O 3.2.0-35-generic #55-Ubuntu
 [ 4750.600197] Call Trace:
 [ 4750.600205]  [<c1560f2c>] ? printk+0x2d/0x2f
 [ 4750.600211]  [<c10b1259>] __report_bad_irq+0x29/0xd0
 [ 4750.600215]  [<c10b14b4>] note_interrupt+0x104/0x150
 [ 4750.600220]  [<c1316736>] ? arch_local_irq_enable+0x7/0xb
 [ 4750.600224]  [<c10af38f>] handle_irq_event_percpu+0x9f/0x1f0
 [ 4750.600229]  [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 [ 4750.600233]  [<c157614d>] ? _raw_spin_lock_irqsave+0x2d/0x40
 [ 4750.600236]  [<c1027518>] ? default_spin_lock_flags+0x8/0x10
 [ 4750.600240]  [<c157614d>] ? _raw_spin_lock_irqsave+0x2d/0x40
 [ 4750.600244]  [<c10af51b>] handle_irq_event+0x3b/0x60
 [ 4750.600248]  [<c10b1cc0>] ? unmask_irq+0x30/0x30
 [ 4750.600251]  [<c10b1d0e>] handle_fasteoi_irq+0x4e/0xd0
 [ 4750.600254]  <IRQ>  [<c157d832>] ? do_IRQ+0x42/0xc0
 [ 4750.600261]  [<c1008bc8>] ? sched_clock+0x8/0x10
 [ 4750.600266]  [<c10701bb>] ? sched_clock_local+0xcb/0x1c0
 [ 4750.600269]  [<c157d770>] ? common_interrupt+0x30/0x38
 [ 4750.600273]  [<c10700d8>] ? profiling_store+0x48/0x60
 [ 4750.600276]  [<c1316736>] ? arch_local_irq_enable+0x7/0xb
 [ 4750.600280]  [<c1317155>] ? acpi_idle_enter_simple+0xf3/0x133
 [ 4750.600285]  [<c144b4dd>] ? cpuidle_idle_call+0xad/0x250
 [ 4750.600289]  [<c100180c>] ? cpu_idle+0x9c/0xe0
 [ 4750.600293]  [<c15455a5>] ? rest_init+0x5d/0x68
 [ 4750.600298]  [<c1834771>] ? start_kernel+0x34d/0x353
 [ 4750.600302]  [<c18343b5>] ? pass_bootoption.constprop.2+0xe2/0xe2
 [ 4750.600306]  [<c18340a9>] ? i386_start_kernel+0xa9/0xaf
 [ 4750.600308] handlers:
 [ 4750.600420] [<f94f3050>] nv_kern_isr
 [ 4750.600423] Disabling IRQ #16