ORA-00604: error occurred at recursive SQL level 1 ORA-12705: invalid or unknown NLS parameter value specified

We faced this issue while connecting to Oracle database Release 10.1.0.5.0 from a Java program [via JDBC]. No probs with the OCI connection, sqlplus is fine.
The reason being, our Language,Country combination in the Regional and Language options[of control panel] doesn't fall under the Fully supported Locales.Hope this helps