This error message is generated when EIGRP receives a Hello packet sourced from an IP address on a
subnet that isn't configured on its receiving interface.
1) Verify that the address of all router interfaces belong to the correct subnet.
2) Check for:
- an incorrect process ID
- an incorrect address or mask
- a missing or incorrect network statement
3) Verify that the routers see each other with show ip eigrp neighbor. Are the routers exchanging Hellos?
4) Is the SRRT 0? If so, the packet hasn't made it through. Are there packets enqueued? No ACK is being received. Is the sequence number 0? If so, no packets have been received from it.
You can filter the debug command debug eigrp packet with debug ip eigrp neighbor process ID IP address (of, say, the neighbor that's not receiving Hellos). This tells it to display only the packets of a particular process ID. (of course, to the router, this may very well be the equivalent of taking a baseball bat to the knees).
Check if the network is configured with two separate subnets on the same physical segment. The routers on one subnet may not be able to communicate with EIGRP routers on the other subnet. This problem can also be seen in networks using improperly configured secondary IP.