My guess is, that you're trying to do that from Enterprise Manager (EM). EM doesn't have any way to find the record you want to delete because it uses record fields in the DELET command WHERE clause and this critirea matches 2 records. You can try to delete it from from Query Analyzer (not tested).

DELETE FROM mytable mt1
  WHERE countrycode = "ABC" AND 
   (SELECT COUNT(*) FROM mytable mt2 WHERE mt2.countrycode = mt2.countrycode) > 1

>Hi All,
>
>I am testing a simple table in a database. I was just using simple country codes and country names from the telephone book. The table has no key set.
>
>I have notice on enry in the table twice, but SQL won't let me delete sending a message:
>
>'Key column information is missing or incorrect. Too many rows were affected by the update.'
>
>I looked this up in help but it is not much help <g>.
>
>Any help would be appreciated.
>
>TIA
>
>Ric