This is because named run in in a jail and, in the jail, there is no such file.
Try to figure out where is the jail. Mine is "/var/lib/named".
Copy your included file to the jail. e.g.
# mkdir /var/lib/named/etc/smbind
# cp /etc/smbind/smbind.conf /var/lib/named/etc/smbind
PS: You do not need to update the path in named.conf.