[c-nsp] error for snmpwalk time out

[teklay gebremichael]

hello, 
i am working on debian lenny OS. and i have installed snmpd but the snmpwalk is not working for me.

i have added the following entries to the snmpd.conf file of the pc i want monitor with nagios

####
com2sec nagiossrv  10.128.5.200 public
####where 10.128.5.200 is my nagios server
group Nagios v1 nagiossrv
####
view all    included .1                                                     
view system included .iso.org.dod.internet.mgmt.mib-2
###
access Nagios ""  any noauth exact all none none

when i use snmpwalk for the debian machine being from the nagios server, the following error is displayed.

 snmpwalk  -v1  -On  -c public  10.128.5.27  .1.3.6.1.2.1.2.2.1.2.1 
Timeout: No Response from 10.128.5.27

but the same command for a switch is working.

 snmpwalk -v1 -On -c mu 10.128.1.1  .1.3.6.1.2.1.2.2.1.2.1
.1.3.6.1.2.1.2.2.1.2.1 = STRING: GigabitEthernet1/1

can any body suggest me wha the problem could be?
thanks in advance
Teklay