Need help to connect to SERVER !!!

Hi Group!, I have a problem connecting from client site to server. I have one server running Oracle 8.1.5, and a client work station in NT. Before, I can connect from my client site to server, and it worked fine. But recently, I couldn't do it anymore. When I try to connect to the server, I got this error :"ORA-12545: Connect failed because target host or object does not exist".
Here is the list of what I DID:
1/ I tried to use Net 8 Easy Config to test the connection from Client site, I got the same error message. 2/ I ran Net 8 Easy Config on the Server with the same service name, it works fine.
3/ I can ping the server from Client site. 4/ I create a new Client service to connect to the Server, I still got the same error.
5/ I start all of the Oracle services from both sites 6/ I looked at the tnsnames.ora, it looks something like this:

# E:\ORACLE\ORA81\NETWORK\ADMIN\TNSNAMES.ORA Configuration
File:E:\Oracle\Ora81\NETWORK\ADMIN\tnsnames.ora
# Generated by Oracle Net8 Assistant

ORACLE =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = Server04)(PORT = 1521))     )
    (CONNECT_DATA =
      (SERVICE_NAME = ORACLE)
    )
  )

Is this problem relate to any network issues?. Does anyone know how to solve this problem?. Any suggestion or ideas are greatly appreciated. Thank you Group!.

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