This is a generic error message which can occur under a variety of contexts with SDE for Oracle. This document will cover two common instances of this error:
1. A Database Theme is created that is the result of a join between an SDE layer and another table in the RDBMS.
2. A Database Theme is classified that is the result of a join between an SDE layer and another table in the RDBMS.
In both cases, the error is due to duplicate field names in the SDE layer table and the join table.
Solution or Workaround
When creating the Database Theme, the final step of the wizard allows for the choice of columns in the tables to be loaded into ArcView. To avoid the error, make one of the duplicate columns unavailable. For example, if both the SDE layer and the DBMS table contain a column named SUB_REGION, uncheck this column in one of the tables.
This error will still occur if an attempt is made to classify the resulting database theme with a field whose name is duplicated in both tables. To avoid this error, create a View in the DBMS which contains all the columns in the DBMS table except for the ones which share the same name in the SDE layer table. When loading the layer using the SQL Query Wizard, join the View to the SDE layer, rather than the DBMS table.