I have the same problem with my 06 QX56, Ive checked the brake fluid level and mine was fine. I have not had a chance to take it to the dealer yet. I read this on infinitihelp .com forum
I had the same thing happen to my '04 when I was doing some slow speed driving in the mall parking lot.
I shut it down and restarted it and it was normal again.
I drove it directly to the dealer and they pulled it into the bay right away. They hooked up the computer to it, installed a (known) firmware update and sent me on my way.
Never happened again.
See the dealer. Infinity will back it I'm sure.
Try searching for this topic on infinitihelp. Hope that helps.