When I try to restart my BIND 9 server under Ubuntu Linux using service bind9 restart or service bind9 start command, I get the following error:
resolvconf: Error: /etc/resolv.conf must be a symlink

How do I fix this problem?

You can fix this error by tying the following command (open a terminal and login as root):
$ sudo -i
# cd /etc
# rm resolv.conf
# ln -s /etc/resolvconf/run/resolv.conf .
# service bind9 restart

Postfix Error

If you get the error as follows (postfix error along with the above error):

 * Stopping domain name service... bind9                                                                                                                                                                                              [ OK ] 
 * Starting domain name service... bind9                                                                                                                                                                                                     
/usr/sbin/postconf: fatal: open /etc/postfix/main.cf: No such file or directory
cp: `/etc/resolv.conf' and `/etc/resolv.conf' are the same file
run-parts: /etc/resolvconf/update-libc.d/postfix exited with return code 1
run-parts: /etc/resolvconf/update.d/libc exited with return code 1

Type the following command:
$ sudo -i
# cd /etc
# mkdir postfix
# touch postfix/main.cf
# rm resolv.conf
# ln -s /etc/resolvconf/run/resolv.conf .
# service bind9 restart