Joe,
Even though the question is a one-liner, there is no quick solution to this problem. Most often, logs about duplicate MAC addresses and excessive flapping of MAC addresses are caused by a switching loop. The first course of action therefore is to double- and triple-check whether there is no switching loop occurring in your network. It would also be helpful to trace down the flapping MAC addresses, going down all ports reported as rapidly learning that MAC and inspecting the switching tables of further switches to see how the MAC address in question got there, possibly tracing out the root cause of the flapping. If using EtherChannels, it is imperative to use LACP or PAgP and avoid the "mode on" EtherChannel at all cost unless absolutely necessary (in cases where the other partner does not support any of these protocols).
This may be a long detective work.
Best regards,
Peter
