The debug crypto isakmp sa command shows the status of the Internet Security Association and Key Management Protocol (ISAKMP) security associations (SAs). The output of this command indicates that the ISAKMP negotiation failed after several retransmissions. The most likely cause of this failure is a mismatch in the authentication key between the two peers. The authentication key is specified by the crypto isakmp key command and must be the same on both routers. If the authentication key is different, the ISAKMP messages cannot be decrypted and verified by the peers, resulting in an error. To fix this problem, the network administrator should verify and correct the authentication key on both routers and clear the existing ISAKMP SAs with the clear crypto isakmp sa command. References: 1, 2, 3, 4