Cause
A data definition language (DDL) statement was issued across a Sharding Replication Unit, but the execution context does not support this DDL statement. This error occurs when the Oracle Database system's synchronous DDL feature is enabled, but the session is not connected using a dedicated server connection. All subsequent attempts at barrier DDL will also be rejected.
Action
Either connect using a dedicated server connection, or, as SYSDBA, disable synchronous DDL and retry the DDL statement.