I have a 3550 switch that is linked to a 4507. Occasionally the link will go into err-disable mode on the 3550 side. It's intermittent, sometime it won't happen for 2-3 weeks, sometimes it will happen twice in a week. I have had this happen before to several 3550 switches but they were always caused by a power outage that lasted longer than the UPS battery run time.
Replace fiber, swap out gbic??????
Logs have shown nothing up until this morning and I received the following:
Mar 28 08:48:28: %PM-4-ERR_DISABLE: link-flap error detected on Gi0/1, putting G
i0/1 in err-disable state