Connection problem

Ok here is one that has me confused. (Yeah, I know that is easy to do)
I have a network of 10 computers and one server in a workgroup. Clients are running Windows 7. Server is a 2003 Enterprise edition. 8 of the clients can connect to my IP of the server for an application share no problem. 2 could not. They could not ping my server, but could ping anything else in the network and communicate with the other clients no problem. Their IPs were configured for DHCP like the others and were given the right addresses, mask, and gateway like the others. But when I changed them to static IPs with different addresses than what DHCP gave out they connected to the server fine. I suspect the IP addresses given by DHCP for the clients were being blocked somehow from connecting to my server. Any suggestions, this has me baffled. I turned off their firewalls and there is no firewall on this server right now. Thanks for help :confused