Not able to login in Linux console as any user

What error message are you seeing, if any?

Does /etc/nologin exist?  If so, delete it.

Check your /etc/pam.d/login   file

#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth       include      system-auth
account    required     pam_nologin.so
account    include      system-auth
password   include      system-auth
# pam_selinux.so close should be the first session rule
session    required     pam_selinux.so close
session    required     pam_loginuid.so
session    optional     pam_console.so
# pam_selinux.so open should only be followed by sessions to be executed in the 
user context
session    required     pam_selinux.so open
session    required     pam_namespace.so
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    optional     pam_ck_connector.so

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Find the /etc/pam.d/login file content.
********************************************************************************************************************
#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth include system-auth
account required pam_nologin.so
account include system-auth
password include system-auth
# pam_selinux.so close should be the first session rule
session required pam_selinux.so close
session include system-auth
session required pam_loginuid.so
session optional pam_console.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session required pam_selinux.so open
session optional pam_keyinit.so force revoke
session required /lib/security/pam_limits.so

#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth required pam_securetty.so
auth required pam_stack.so service=system-auth
auth required pam_nologin.so
account required pam_stack.so service=system-auth
password required pam_stack.so service=system-auth
session required pam_stack.so service=system-auth
session optional pam_console.so
session required pam_limits.so
******************************************************************************************************
I am able to resolve the problem by commenting the following line.
session required /lib/security/pam_limits.so

But unable to understand why this line is creating the problem since this line has been added as per the installation procedure of Oracle 10g R2

Ah, and try just pam_limits.so instead of /lib/security/pam_limits.so ...

Thanks Mushy..It worked..Can you tell me the use of the same?

Not sure what you mean; if you mean how to use the pam_limits features, have a look in /etc/security/limits.conf, my copy is fully self-documented, loads of comments to tell you how to use it.  It's used to limit users to certain amounts of CPU time, memory space, number of simultaneous logins, priority of user processes, etc.