Did you ever resolve this problem? I am having the same problem after moving the machine. So far I have replaced the USB cable to the I/O board and reseated the power cable at both ends to the I/O board. I also verified the 5 and 12 volt supplies to the I/O board are not too low. I also intend to look at them on a scope to see if they are clean but have not done that yet.
I have not seen it again since doing that but it's only been a few days and it was intermittent so not sure if I solved it or not.