Ok there are 2 fixes for this depending if you running bind as chroot or not.
If you are running bind chroot the pid location is at
/var/run/named/named.pid
if you running bind under /etc/bind/ or non-chroot the pid location is at
/var/run/bind/run/named.pid
You can fix the locations under Webmin -> Servers -> BIND DNS Server -> Module Config -> System configuration