not able to connect the oracle database through database reader

I am not able to connect through database reader with oracle crendntial. I am able to connect the oracle with same userid and password.The following error i am getting while connecting through database reader
"java.sql.sqlrecoverableException:I/O execption:network adapter could not establish the connection" 
for connection i am using the ojdbc6.jar in oracle client 
In the database reader, I have entered the following entries --
database driver - oracle.jdbc.oracledriver
database url - jdbc:-Oracle:thin:@//<host_name>:1521/<servicename> 
I am able able to connect the database through same configation from one location
but not able to connect from different location. Listener is up for both cases.
I am connecting from both location through VPN. 
Please suggest. 


I guess this is a network issue if you can connect to the database in one location but not at the other location. have you tryed to ping the database from the location where you can not establish the connection?