PROBLEM
On my Linux system:
* dhcp and tftp is running on same system - tftp-dhcp-server
* tftp-dhcp-client is able to get IP address from DHCP server but tftp fails with below message
$ tcpdump |grep ICMP
3:54:09.379106 IP tftp-dhcp-server > tftp-dhcp-client: ICMP host tftp-dhcp-server unreachable - admin prohibited, length 80
03:54:19.320800 IP tftp-dhcp-server > tftp-dhcp-client: ICMP host tftp-dhcp-server unreachable - admin prohibited, length 85
03:54:55.351027 IP tftp-dhcp-server > tftp-dhcp-client: ICMP host tftp-dhcp-server unreachable - admin prohibited, length 85
FIX
$ service iptables status
$ service iptablesstop
$ chkconfig iptables off
* If above did not help, checkif firewal is blocking tftp request.
