LinuxQuestions.org - unable to fetch archives

anto@anto-laptop:~$ sudo apt-get install openssh-client
[sudo] password for anto:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
libpam-ssh keychain openssh-blacklist openssh-blacklist-extra
The following packages will be upgraded:
openssh-client
1 upgraded, 0 newly installed, 0 to remove and 430 not upgraded.
Need to get 762kB of archives.
After this operation, 0B of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
openssh-client
Install these packages without verification [y/N]? y
Err http://in.archive.ubuntu.com/ubuntu/ lucid-updates/main openssh-client 1:5.3p1-3ubuntu7
Something wicked happened resolving 'in.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://in.archive.ubuntu.com/ubuntu/...untu7_i386.deb Something wicked happened resolving 'in.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
anto@anto-laptop:~$

Why does it come like this?
Should I do any changes in /etc/apt/source/list?
Please do help me...