"booting disallowed" in server log

[Matt Laoye]

I've posted the question several days ago and got no reply, this is
happening on our network every day, usually within large
networks, /22 in the following example, restart server
fix the problem. Also I don't think it's client issue, since it happens to
many different clients. Can someone explain to me why the server denied
booting to the DHCPDISCOVER while it ACKed a lease to the same host
in less than a minute ago?
Apr  5 12:50:58 omni dhcpd: DHCPREQUEST for 10.235.99.118 from
00:14:a5:e5:7f:67 (krystle) via 10.235.96.100
Apr  5 12:50:58 omni dhcpd: DHCPACK on 10.235.99.118 ends
2007/04/05:17:50:58 to 00:14:a5:e5:7f:67 (krystle) via 10.235.96.100
Apr  5 12:51:21 omni dhcpd: DHCPDISCOVER from 00:14:a5:e5:7f:67 via
10.235.96.100: booting disallowed
Apr  5 12:51:59 omni dhcpd: DHCPDISCOVER from 00:14:a5:e5:7f:67 via
10.235.96.100: booting disallowed

host registered through omapi in dhcpd.leases:

host hostname{
  dynamic;
  hardware ethernet 00:14:a5:e5:7f:67;
}

Here is the relevant dhcpd.conf, we are running ISC dhcp V3.0.5:

shared-network service-building {
        subnet 10.235.96.0 netmask 255.255.252.0 {
                option routers 10.235.96.100;
                option broadcast-address 10.235.99.255;
                option subnet-mask 255.255.252.0;
                default-lease-time 3600;
                max-lease-time 3600;
                pool {
                        deny unknown clients;
                        range 10.235.96.2       10.235.99.254;
                }
        }
        subnet 10.10.14.0 netmask 255.255.254.0 {
                option routers 10.10.14.1;
                option broadcast-address 10.10.15.255;
                option subnet-mask 255.255.254.0;
                default-lease-time 300;
                max-lease-time 300;
                pool {
                        deny known clients;
                        range 10.10.14.5      10.10.15.254;
                }
        }
}


Let me know if you need more info,

Thanks,
Matt