Daniel,

To look for corruption you can

select distinct TheColumn ;
   from TheTable ;
   into table c:\temp\allvalues ;
   order by TheColumn

browse the result and look for out-of-the-norm values.

How many rows are you trying to remove from the table with the UNIQUE index? Does it matter what row survives and which ones are removed?

Since you are making a single pass through the table you can actually use a scan about as fast as a select. Something like this:

select * from TheTable into table c:\temp\UniqueCopy where 1=2
create table pks ( TheColumn i )
select pks
index on TheColumn tag TheColumn
select TheTable
scan
   if ( ! indexseek( .f., "pks", "TheCOlumn" ) )
      insert into pks values ( TheTable.TheColumn )
      insert into UniqueCopy values ( TheTable.TheCOlumn, TheTable.... )
   endif
endscan

>I get the same error from VFP. By the way I have version 7. How do I know if I have data corruption? I have aover 5 million records. How do you remove duplicates or create a unique query with sql select?