Hi,
Most likely there is a bridge loop somewhere in your network.
Do u also receive messages from your switches that there is mac addresses flapping between ports on your switch?
If yes, then most likely there is a loop in your network. Track down the switch that is producing most of these mac addr flapping error messages.
Refer to the link below for more details on the error message.
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml#t20
Let me know if it helps.
