It doesn't make sense. I don't know why the PXE boot would fail after a successful reboot. I still haven't found what this means:
dhcpd: DHCPRELEASE of 10.1.1.155 from 00:40:63:e5:77:1a via eth0 (not found)
More trouble shooting...
Could you provide us with your dhcpd.conf file (minus any sensitive info)? It may be something in the config.