Can't get list sorted by date. How to show data ordered by date?

XDocument doc = XDocument.Load(Server.MapPath("file.xml"));
IEnumerable<XElement> items = from item in doc.Descendants("item")
                                      orderby Convert.ToDateTime(item.Attribute("lastChanges").Value) descending
                                      where item.Attribute("x").Value == 1
                                      select item;

        Repeater1.DataSource = items;
        Repeater1.DataBind();

Xml file looks like this:

<root>
  <items>
    <item id="1" lastChanges="15-05-2010" x="0" />
    <item id="2" lastChanges="16-05-2010" x="1" />
    <item id="3" lastChanges="17-05-2010" x="1" />
  </items>
</root>