nmap failing on the mac

[robin at digininja.org (Robin Wood)]

Both myself and a friend have had the same problem with nmap, I'm on
the local network and I can ping some machines, the network is up and
working fine but at some point through an nmap ping scan I start to
get "No route to host" messages as below:

root# nmap -sP 192.168.200.0/24

Starting Nmap 5.30BETA1 ( http://nmap.org ) at 2010-06-04 13:50 BST
Nmap scan report for 192.168.200.0
Host is up (0.0068s latency).
Nmap scan report for 192.168.200.1
Host is up (0.0018s latency).
MAC Address: 34:EF:44:29:B3:79 (2Wire)
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.18, 16)
=> No route to host
Offending packet: ICMP 192.168.200.33 > 192.168.200.18 Timestamp
request (type=13/code=0) ttl=45 id=27161 iplen=10240
Sleeping 15 seconds then retrying
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.18, 16)
=> Host is down
Offending packet: ICMP 192.168.200.33 > 192.168.200.18 Timestamp
request (type=13/code=0) ttl=45 id=27161 iplen=10240
Sleeping 60 seconds then retrying
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.21, 16)
=> No route to host
Offending packet: ICMP 192.168.200.33 > 192.168.200.21 Timestamp
request (type=13/code=0) ttl=58 id=52667 iplen=10240
Sleeping 15 seconds then retrying
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.21, 16)
=> Host is down
Offending packet: ICMP 192.168.200.33 > 192.168.200.21 Timestamp
request (type=13/code=0) ttl=58 id=52667 iplen=10240
Sleeping 60 seconds then retrying
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.22, 16)
=> No route to host
Offending packet: ICMP 192.168.200.33 > 192.168.200.22 Timestamp
request (type=13/code=0) ttl=52 id=43894 iplen=10240
Sleeping 15 seconds then retrying
sendto in send_ip_packet: sendto(4, packet, 40, 0, 192.168.200.22, 16)
=> Host is down
Offending packet: ICMP 192.168.200.33 > 192.168.200.22 Timestamp
request (type=13/code=0) ttl=52 id=43894 iplen=10240
Sleeping 60 seconds then retrying

The network is still there and I can still ping other machines
straight after I kill nmap:

root# ping 192.168.200.1
PING 192.168.200.1 (192.168.200.1): 56 data bytes
64 bytes from 192.168.200.1: icmp_seq=0 ttl=255 time=1.877 ms
64 bytes from 192.168.200.1: icmp_seq=1 ttl=255 time=1.438 ms

I've only used this beta version but the friend who has seen it has
used various previous versions so it isn't just an issue with the beta
version.

Has anyone else seen this and do you know how to fix it?

Robin