Recently our headquarter upgraded our ACS server from version 4.2 to 5.2 with a new IP and system. I am updating the new tacacs-server host IP and key to my local switches. When I typed in the command : tacacs-server host x.x.x.x key xxxxx , the switch locks up instantly and shows authentication fail. I had to reload the switch, disconnect from the network, login with local account on the switch then proceed to enter the tacacs command. Reconnect to network and it works. I still have 5-6 more switches to update and don't want to disconnect them from live network just to type in the command. Need help. Thanks.