Oracle Message ORA-02329 - column of datatype string cannot be unique or a primary key

ERRORcolumn of datatype string cannot be unique or a primary key
CAUSEAn attempt was made to place a UNIQUE or a PRIMARY KEY constraint on a column of datatype VARRAY, nested table, object, LOB, FILE or REF.
ACTIONChange the column datatype or remove the constraint. Then retry the operation.