Delete node from from xml with Linq

I am trying to delete a node if name is corresponding but I get a NullReferenceException in foreach statement. Here is the xml structure:

<Items>
    <channel>
    <region>test</region>
    <name>testname</name>
    <oldposition>0</oldposition>
    <newpostions>0</newpostions>
  </channel>
</Items>

And here is how I try to delete the node:

private void removeFromXml(string buttonname)
        {
            XDocument doc;
            using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
            {
                if (isoStore.FileExists("favorites.xml"))
                {
                    using (IsolatedStorageFileStream isoStream = new IsolatedStorageFileStream("favorites.xml", FileMode.Open, isoStore))
                    {
                        doc = XDocument.Load(isoStream);
                    }
                    Debug.WriteLine(doc.ToString());
                    var q = from b in doc.Descendants("channel") select b;
                    foreach (XElement xe in q) //here is the error described below
                    {
                        if (xe.Element("name").Value.ToString() == buttonname)
                        {
                            xe.Remove();
                           Button bt = (Button)favorites1.FindName(buttonname + "fav");
                           favorites1.Items.Remove(bt);
                        }
                    }

                    using (IsolatedStorageFileStream isoStream =
          new IsolatedStorageFileStream("favorites.xml", FileMode.Create, isoStore))
                    {
                        doc.Save(isoStream, SaveOptions.OmitDuplicateNamespaces);
                    }
                }
            }
        }

I get this error on foreach statement :

An exception of type 'System.NullReferenceException' occurred in System.Xml.Linq.ni.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.