Network Inconsistencies

To start off, this is all through a VPN. When connected through thte VPN I am able to see all of my machines as described and I can telnet to all but 4 boxes (UNIX and LINUX OS on these). I cannpt ping these same 4 boxes or see them at all. My problem really is that if I PCAnywhere into one of the other boxes on this network, I can reach these 4 boxes from them, just not through my VPN client box. I dont really understand what is causing this denial from everywhere on this network and not from a VPN’ed system.