Just a small tip that will help you to avoid to loose half a day looking for a solution…
When using Sharepoint throught web services remember to set the WEB REFERENCE to the right website.
If you have to access the main website point to http://<typehereyourdomain>/_vti_bin/lists.aspx but if you need to work on a subsite, remember that you have to point to the right web service, i.e. http://<typehereyourdomain>/<typehereyoursubsite>/_vti_bin/lists.aspx.
