Thanks for the clue CLOS. I was able to fix my problem. I have NortonAntivirus on all of my PCs. It has got 3 modes of network protection: Full Trust, Shared and Restricted. On the Main comp I changed my network PCs status from Shared to Full Trust. On rest of the network PCs, Main comp was already marked as Full Trust. As you have mentioned I wasn't able to ping Main comp from networked PCs with Shared status. With Full Trust status I was able to ping Main comp and connect to its AC database from networked PCs with out any problem on first click.
I would suggest others with similar problem should modify their firewall settings accordingly to clear this issue.
Thank you.
-Rao
