Named fails to start with error the key is invalid:
# /etc/init.d/named status
WARNING: key file (/etc/rndc.key) exists, but using default configuration file (/etc/rndc.conf)
rndc: connection to remote host closed
This may indicate that
* the remote server is using an older version of the command protocol,
* this host is not authorized to connect,
* the clocks are not synchronized, or
* the key is invalid.
Rndc secret key does not match in
Make sure that rnds key is the same in
# less /etc/named.conf |grep secret
# less /etc/rndc.conf |grep secret
If secret key does not correspond, update one of these files and set the same key.