Underscores in domain names
If a domain (or more likely a subdomain) contains an underscore, bind will not start unless the following statements are added to the named.conf file:
check-names master ignore;
check-names slave ignore;
There are security risks associated with setting these parameters which will disable name-checking, more information here and here and here.
Another alternative may be to parse and delete lines with underscores.
(Thanks to Will M. and Mike P. for the info).