So... what do you guys make of these messages:
[2014-01-29 11:49:42] HFB 12: Bad CRC 0 vs 159, discarding packet
[2014-01-29 11:49:43] HFB 12: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:43] HFB 12: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:43] HFB 12: Bad CRC 0 vs 159, discarding packet
[2014-01-29 11:49:44] HFB 12 HFGetHeader usb read err:(-9) LIBUSB_ERROR_PIPE
[2014-01-29 11:49:44] HFB 12: device disappeared, disabling
[2014-01-29 11:49:44] HFB 12 failure, disabling!
[2014-01-29 11:49:49] Accepted 67770695 Diff 633/512 HFB 11
[2014-01-29 11:49:51] Hotplug: Hashfast added HFB 13
[2014-01-29 11:49:51] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:51] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:51] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:51] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:52] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:53] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:54] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:54] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:54] HFB 11: Bad CRC 0 vs 178, discarding packet
[2014-01-29 11:49:54] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:54] HFB 11: Bad CRC 0 vs 175, discarding packet
[2014-01-29 11:49:55] Accepted 6dcaae63 Diff 597/512 HFB 13
[2014-01-29 11:49:59] Accepted 5e7269c3 Diff 694/512 HFB 11
[2014-01-29 11:50:00] Accepted 7d2a89d4 Diff 524/512 HFB 11
Looks to me like USB communication issues.