ORA-01409: NOSORT option may not be used; rows are not in ascending order
Cause: Creation of index with NOSORT option when rows were not ascending. For non-unique indexes the rowid is considered part of the index key. Therefore, if you create an index nosort and two of the rows in the table have the same key and are stored in ascending order, but get split accross two extents where the dba of the first block in the second extent is less than the dba of the last block in the first extent, then the create index nosort may fail.
Action: Create the index without the NOSORT option, or ensure table is stored in one extent.