Hi Siddharth:
You don't say which LDAP server that you are using. If this is AD ,Looks like you are failing in authorization. . Yes the four users are in users.xml. See teh Security Guide for details
May also want to check this part
</property>
<property name="groupObjectQuery">
<value>(&(objectClass=group)(cn={0}))</value> -- HERE
</property>
<property name="useSSL">
<value>false</value>
</property>
<property name="plainTextPasswords">
<value>false</value>
</property>
<property name="groupMemberQuery">
<value>(&(objectClass=group)(member=%u))</value> -- OR HERE
Work with your LDAP Admin to check all is okay on LDAP side