Rss feed - displays duplicate items

I'm creating my own RSS files (XML) (c#.NET) to publish something and I'm using Outlook RSS to read them some of my friends too. It works ok, but sometimes for some reason I get duplicate items suddenly. When I look at the XML files I see their sinlge entries (not double).

I read posts in 2008 and 2010 which have the same problem. Now we are in year 2011 does Outlook still have this problem ?

1) Is it still true that Ms Outlook 2010 still gives that problem ?

2) I'm creating the XML files self so what do I need to change to avoid this issue?

I keep the published date on a table...

pubDate = (item.date_published == null) ? System.DateTime.Now.ToString("o") : Convert.ToDateTime(ite开发者_Python百科m.date_published).ToString("o");

Check if your items have unique identifiers (preferably GUIDs) and that a single item receives only one identifier.