Hi,
You cannot iterate through the drop down list when you enter that values manually. When you use
XPathNodeIterator iter = root.CreateNavigator().Select("/my:myFields/my:field4",NamespaceManager);
you will get only the value selected not all the values in the drop down list. If you want to iterate the values then you need to place the values in an xml file and look up values from an external data source in the drop down.