Are you connecting with the same username/password locally on the server that you are using to connect from the client? Check the tnsnames.ora on the client to ensure that the service name is pointing at the correct SID and server. It's possible that your service name is pointing to another database on another server which you have no access to with the username/password combination you are providing.
A more likely possibility is that you may need to install a newer client. Net8 is quite a few releases behind Oracle 10g so you may need to at least install the 9.2 client to connect to your Oracle 10g database. To confirm this, you can review Doc ID # 207303.1 if you have access to Metalink or open a TAR with Oracle Support.
Dig Deeper on Oracle database installation, upgrades and patches
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