You do not mention what version of LDMS you are running. A couple of things this could be is, the LANDesk agent on that server is not an 8.8sp4 or LDMS 9 or higher agent, or the Server is acting as a DHCP server, if that is the case you can not have DHCP and PXE on the same server.
I'm running LDMS 8.8 with sp4. Although the server is a DNS server it is not a DHCP server and no DHCP services other the DHCP client service is running. FYI, I seem to have the same problem when trying to install PXE Rep on a Windows 7 machine.
did you check if the following UDP ports be open on the server and on the firewall:
Port 69 (TFTP)
Port 4011 (PXE)