Vista Activation Error – 0x8007232B, DNS name does not exist

I m running Vista Enterprise and willing to Activate On-Line.
I m using Cable Net (VPN) with some auto IP and DNS server settings. I have manually configured IPv4 properties for IP and DNS server entries by checking my LAN properties for these.
But still my problem is there when Activating Vista On-line.
Can any friend suggest me any solution for that ? OR is it a bug in Vista ? or something else ?