snmp issue - Timeout: No Response from localhost

Hi every one,

We are monitoring resources with nagios using snmp plugins.

I am facing issues on few machines but rest all are ok. They have the same config but I don't know what is wrong.

I tried as much as I could but couldn't fix it.

Here is the rpms installed on this client

[root@w2 ~]# rpm -qa | grep snmp
net-snmp-libs-5.3.2.2-7.el5_4.2
net-snmp-5.3.2.2-7.el5_4.2
net-snmp-utils-5.3.2.2-7.el5_4.2

The config file is
[root@w2 ~]# cat /etc/snmp/snmpd.conf
rocommunity secret

[root@w2 ~]# lsof -i :161
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
snmpd 13458 root 10u IPv4 292733053 UDP *:snmp

[root@w2 ~]# /etc/init.d/snmpd status
snmpd (pid 1345 is running...

but when I test

[root@w2 ~]# snmpwalk -v 1 -c secret localhost .1.3.6.1.2.1.1.1.0
Timeout: No Response from localhost
[root@w2 ~]# snmpget -v1 -c secret 127.0.0.1 system.sysDescr.0
Timeout: No Response from 127.0.0.1.

See the output on one of the other client where it is working

[root@w5 ~]# snmpwalk -v 1 -c streamuk localhost .1.3.6.1.2.1.1.1.0
SNMPv2-MIB::sysDescr.0 = STRING: Linux w5.mycompany.com 2.6.18-164.9.1.el5 #1 SMP Tue Dec 15 21:04:57 EST 2009 i686
[root@w5 ~]# snmpget -v1 -c streamuk 127.0.0.1 system.sysDescr.0
SNMPv2-MIB::sysDescr.0 = STRING: Linux w5.mycompany.com 2.6.18-164.9.1.el5 #1 SMP Tue Dec 15 21:04:57 EST 2009 i686

The same config is working for all clients but have problems with few machines. May be I am doing something wrong in config or testing at very basic level.

Can any body help me to sort this out please?

Many thanks.