We get an error "%CLNS-3-BADPACKET: ISIS: LAN L1 hello, Duplicate system ID" on each of our 2 6500 switches running ISIS. The system ID's have been checked and are fine. A 802.1q trunk connects the two switches. We get the error every 60 seconds for 7-8 minutes in a row about every 2-3 hours.
There is no information on this error on Cisco's website. MTU size is fine on each switch.