Error received when a simple select is executed to query data from a audit table:
"OCI-21500 - internal error code, arguments [koiocon: opq]."
Older XDB clients connecting to newer servers (eg: Oracle 9i client connecting to 10g server) fails with an OCI-21500 error due to new properties added to the root schema.
Upgrade the Oracle client to the same version as the server.
Refer to Oracle's Metalink and review DocID:3075419.8.