When using ArcCatalog's Spatial Database Connection dialog to establish a direct connection to an Oracle server, the following error occurs:
"Failed to connect to the database. Column index not found[ ]" followed by "Unable to open the selected database (with the current connection properties)."
The ArcGIS client version is incompatible with the sdesetupora8i version executed on the server. The sdesetupora8i executed on the server must be the same version as the client attempting to establish the direct connect.