Thanks weevil for the response. Even though i verified the logs the way how you mentioned, there was no sufficient info which helped me to resolve the issue.
So i decided to play around the various other settings and then when i just changed the IP address with first dc domain name under Manager Domains, it started working fine. So what i am guessing is that, the issue would bewither with the DNS configuration of first dc or with the PGP UN itself (as PGP Gateway may not really work if domain name is NOT mentioned under Managed Domain section in Consumer Policy). Not sure about the exact reason, but the issue is resolved in my case :)