I have a 6506 incrementing FCS-ERR counters on an SFP port. The other end of the fiber is connected to a Catalyst 2980. There are no errors on the 2980 port and there is no duplex mismatch noted on either switch port. What would be the most likely cause of these errors as it does seem to be impacting performance? My first inclination is the SFP gbic on the 6506 is bad.