Hardware :: Nvidia Co-processor Probe Failed With Error -1

I'm looking through dmesg and see

Code:

nvidia: probe of 0000:00:03.5 failed with error -1

the corresponding bus is

Code:

00:03.5 Co-processor: nVidia Corporation MCP79 Co-processor (rev b1)
Subsystem: nVidia Corporation Device cb79
Flags: 66MHz, fast devsel, IRQ 16
Memory at 93300000 (32-bit, non-prefetchable) [size=512K]
Kernel modules: nvidia

from where I infer that the module is correctly loaded though. Do you guys know what is the -1 error code? is there any way I could check if the coprocessor is currently working?