You can only have one object with a name in a schema. There is probably another object with the same name.
Code:
SELECT owner, object_name, object_type, status
FROM all_objects
WHERE object_name='TABLE_POSITION_A_IDX2';
The other possibility is that if you have the recycle bin on, you could try purging the recycle bin, before creating the index.
Code:
PURGE dba_recyclebin;
If you want to know what indexes exist on a table try this:
Code:
SELECT index_owner, index_name, column_name, column_position
FROM dba_ind_columns
WHERE table_name='TABLE_POSITION_ADJ'
ORDER BY 1,2,4;