If you configure a key on the Content Engine, it must be the same as the one configured on the TACACS+ servers. The TACACS+ clients and servers use the key to encrypt all TACACS+ packets transmitted. If you do not configure a TACACS+ key, packets are not encrypted. TACACS+ authentication is disabled by default. You can enable TACACS+ authentication and local authentication at the same
Still you are getting problem then
Delete the configuration.
Restart the router and configure again.