We've seen this message and a message saying that the tapmux (tmux) ASIC was being reset ("HwCheck: Clock Recovery Failed Reset tmux ..."). The two ASICs are related and the folks at Nortel say that its a reason to be concerned if errors happen more than 3 times in a given 5 minute period or more than 10 times in a 24 hour period. Here's a cut-n-paste of some of their explanation, it sounds like a swip reset is more serious than a tmux reset but that both may happen from time-to-time.
"Clock Recovery Failed Reset tmux on one of the slots - The 'Clock recovery' happens when the timing on the backplane is re-synchronized. For this message,
the clock synchronization attempts failed on the tmux for one of the slots of the switch in concern. This error can occur and if severe enough, the software will take necessary actions to reset the appropriate ASICs (i.e., SWIP and TapMux).
"Each I/O module is connected to the switch fabric via
the backplane; to avoid data corruption the software monitors the data integrity between the I/O modules and the switch fabric. In case an error is detected between these 2 parts, the software will check out the traffic in the next seconds, if there is no new errors, no action will be taken, if a new error is seen the software will reset the switch fabric ASICs (swip) and the tmux ASICs, a warning message saying the swip has been reset will be logged. In our situation, this is not the case, there is no swip reset in the log, which means no data have been corrupted, just clocking/synchronization issue occurred once.
"You would see as well some warning messages in the log in case some data were corrupted (for example bad cells due to bit errors), the conclusion would be the same, which means unless there is a lot of these warning messages it
does not mean that there is a real hardware problem.