"zone already exists" error preventing reload

[William R. Dickson]

There is one particular domain that, when added to named.conf,  
prevents a reload. The error is:

/usr/local/namedb/named.conf:72228: zone 'foo.com': already exists

I've received this error before when a coworker has somehow managed  
to add a domain twice. So I went looking for the duplicate...and  
couldn't find one!

root at oak# grep foo.com named.conf
named.conf:zone "foo.com" {
named.conf:     file "dbfiles/foo.com";

But sure enough...commenting out the record in named.conf stops the  
error from occurring, and named can still serve up responses for the  
domain!

I'm stumped...haven't found a similar issue in the list archives or  
via google. Any ideas?

Thanks,

-Bill