C#: Error occuring when I want to save a file via SaveFileDialog?

I Have a little problem with my C# code.

In my method, I create a XDocument/XML-File and after that, I want to save it via SaveFileDialog. It works everything fine until I click the "Save"-Button in the Dialog and then an error appears, which says "The File C:\Users\User\Desktop\XMLOutput.xml is not existing. Check, if the correct file name was indicated."

So here is my code:

public void Create_XMLFile()
    {
        XDocument xDoc = new XDocument(
            new XElement("itemlist",
                new XElement("item",
                    new XAttribute("article", "1"),
                    new XAttribute("quantity", "200"),
                    new XAttribute("price", "35")))
        );

        SaveFileDialog saveFileDialog = new SaveFileDialog();
        saveFileDialog.InitialDirectory = "C:\\";
        saveFileDialog.CheckFileExists = true;
        saveFileDialog.CheckPathExists = true;
        saveFileDialog.DefaultExt = "xml";
        saveFileDialog.Filter = "XML (*.xml)|*.xml|All (*.*)|*.*";
        saveFileDialog.FilterIndex = 2;
        saveFileDialog.RestoreDirectory = true;
        saveFileDialog.FileName = "XMLOutput";

        if (saveFileDialog.ShowDialog() == DialogResult.OK)
        {                
            xDoc.Save(saveFileDialog.FileName);
        }
    }

// Button, which triggers the method above
private void Export_Click(object sender, RoutedEventArgs e)
    {
        Create_XMLFile();
    }

So yeah, where is the problem in my code? I simply want to safe the XML-File in which path the user selected. But as I said, I always get this error message, after I Click the "Save"-Button in the Windows-Dialog. :(

Hope you guys can help me here.