Unable to establish contact with session – PXE

Trying to get PXE boot to work. I have win2003 server, TFTPD32, DNS and DHCP configured.
Ghostcast server process works no problem when I boot client from floppy disk. However, when booted from NIC, I get the dreaded unable to establish… message.
Client is assigned an IP and I can ping it from server. The TFTP session indicates that the “Peer returns ERROR ”
Would appreciate some troubleshooting tips.