Found this in the Cisco IOS 15.1M manuals today
The goodbye message is a feature designed to improve EIGRP network convergence. The goodbye message is broadcast when an EIGRP routing process is shut down to inform adjacent peers about the impending topology change. This feature allows supporting EIGRP peers to synchronize and recalculate neighbor relationships more efficiently than would occur if the peers discovered the topology change after the hold timer expired.
The following message is displayed by routers that run a supported release when a goodbye message is received:Apr 26 13:48:42.523: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.1.1 (Ethernet0/0) is down: Interface Goodbye received
A Cisco router that runs a software release that does not support the goodbye message can misinterpret the message as a K-value mismatch and display the following message:Apr 26 13:48:41.811: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.1.1 (Ethernet0/0) is down: K-value mismatch
Obviously, the signalling to a neighbor that a protocol has been gracefully shutdown means good things for protocol convergence and loop prevention in a Distance Vector protocol. The point that I think is important is that a network that has some IOS 15.1M and more mainstream sofware might see error messages about K-value mismatch and think that something is broken. In this case, the error message is exactly correct, and can be safely ignored.
As always, It Depends™ on your exact configuration, its possible that someone has actually configured K-values (but it’s unlikely these days) and the message is telling you.