Warning: Unique index on non-OID field

This layer or table has an unique attribute index on a field other than the ObjectID field.

Solution: Non-system fields that are user managed cannot have unique attribute indexes. Use the Catalog window or ArcCatalog to remove the unique index from the field. The index could be in the feature class you are trying to edit or, if the feature class is in a feature dataset, it could be in another feature class in the feature dataset.