%C6KERRDETECT-2-LPBKFAIL: The in-band loopback test between switch processor and route processor failed, count:[dec]
This indicates that the system detected an unrecoverable in-band loopback test error. [dec] is the number of times that the system detected the failure.
The system continuously monitors the communication between the route processor (RP) and the switch processor (SP) on a given supervisor. If ten consecutive pings are missed between the RP and the SP, it is noted that there is some problem in the communication between them, and the switchover is initiated, if a redundant supervisor is available.
The communication between the RP and the SP can be broken for many reasons, sometimes it is a transient issue.