While in the Navigator window you are experiencing: ORA-01460: unimplemented or unreasonable conversion requested.
Make sure you are using the latest version 4.3.2-476 the new version better supports Oracle 9i database.
ORA-01460 is usually related to the database that have a character set of UTF-8 or multibyte. Currently, SQL Navigator is not completely compatible with UTF-8 character sets, but is tolerant.
The following option help to resolve your error.
1. Open a connection window.
2. Select the Options button.
3. Place a check mark in the "Use OCI7 for this connection" option.
4. Connect to the database.
Click on the Options button at login, and for the "bytes per character", set this to 3.