I think it's because you have to have a PTR record for your V-Center box normally. Or the VCSA depending on the version you're installing.
https://en.wikipedia.org/wiki/Reverse_DNS_lookup
provides a good starting point for researching how PTR records work, also for crafting correct tests to verify your PTR record is working.
Morning,
Gotta ask this rather basic question... Why do you not have a DNS server? Could you give some more details about the setup?
Thanks
Alex