For IRC servers, it is not enough that your IP address can be resolved a hostname. The IRC server also checks that that hostname can be resolved back to that same IP address. That two-way check prevents hostname spoofing, because it is relatively easy to make a privately owned IP address resolve to, say, fbi.gov.
I would guess that in your case, the problem is in the host-to-IP part of the check. If that is indeed the case, only Google can fix that issue for you.
