What prevents Sequel pro from deleting found records in some queries?

[Allen]

I've got a table where each value in column one should only have one match from column two. However, duplicates have been created.

If I perform this search:

select * from `table_one` where `column_one` = "1400" order by  `colummn_two` asc, `column_three` asc

Then I can easily see the duplicates, however, sequel pro won't let me delete any entries.

What am I doing, that makes sequel pro think it can't delete entries from the found set?

Thanks!