I got the issue resolved.
Previous AD configuration:
Domain: <NETBIOS>
User: <NETBIOS>/<USER>
Modified Configuration:
Domain: <NETBIOS.DOMAIN>
User: <USER>
I made these changes as I see in the netlog inside the guest os trying to connect with AD as user "<NETBIOS>/<NETBIOS>/<USER>
As you see, by default it is pulling domain for user account from domain attribute. So we don't have to give domain or NetBIOS before user name! BASICS! 
Thanks a lot...
Hari.