Oracle Database Discussions

Hello.i am working with a software house in which i had recently developed a project for NGO i.e Research Monitoring Evaluation.they have 5 different zonal offices in 5 different cities and a head office.
now they want entry to be done from zonal offices but the data should be store at head office.the procedure that i have adopted for this task is like turning the listner on over server and making the configurations set on client using Net 8 assistant exactly like in a network environment.but here in order to get the server available we are using dial up vpn utility because of head office being in another city.
But when i test it and connect the form
example
username ="Scott" password="tiger" and database="kaash"
kaash is the name of server.but i get reply Tns no listener ora-12224.
as listner over the server has been started.
A clear guide line is required from the start.An immediate response will greatly be appreciated
Thank you
Hamad Salahud-din