I came across an error today in SQL Server 2005. The row value(s) updated or deleted either do not make the row unique or they alter multiple rows. The reason I got this error was because I created a table for a data mapping application and in my haste I forgot to include a primary key. I checked my table today and found records that were duplicated and whenever I tried to delete or edit a row in SQL Management Studio this error showed up. So I knew I had to put a primary key in the database and in order to do that I had to take care of the duplication.