From: sed on
I am seeing the same problem.  I am trying to use the 8451 to log SMBus communication with a smart battery over a period of several months, but it will not even run for one hour without some sort of communications problem that the 8451 cannot recover from. 
 
I am running the bus at 32kHz, I have tried other frequencies but the problem seems to be frequency independent.
 
I have also tried making sure nothing else is using USB (on any port) at the same time in my program and that seemed to improve the time between failures. I am also using a NI USB-6210 for voltage & current measurement.
 
I am trying to capture the problem on a scope to work out what is going wrong.