I've got the same/similar setup(hub/pi/bfgminer).  when i plugged in 7 sticks i had 2 give problems.  one was puking errors and the other refused to hash.

i unplugged 1 stick and started a fan blowing across the 6 USB sticks.  the 1 stick which was previously giving >10% hw errors started hashing normally.
the 6 sticks even after not clearing errors are now averaging ~1% hw errs over 30 hours now.  the actual rate should be much lower once i restart and clear the counters.  i measured the sticks at 140 degrees F without the fan.  with fan they're comfortable to the touch.