VS 2005 Importing Data Not Working?

I have a table in my database. I have an import routine which reads rows from and XML file. It first loops through my existing table to see if the row exists using a date and store code column as a unique id. It all works fine until this senario occurs.First file is read in and a new row is added for 01/03/2011, store code 100. The second file is read in which also has a row with 01/03/2011, store code 100. But when I loop through it does not find the row I just added so it adds it again.The only solution I can think of is to re-populate the local table everytime I add a new row but this will have a massive amount of over heads.If I add a row to an existing dataset surely if I loop through that dataset I should come across it.