UWLException: (Default) Logged in users context or session doesn't exist

hi

i tried create a web dynpro project, and access uwl, like the document

Accessing UWL Notifications from Web Dynpro Using UWL API

but doesn't matter i tried

IUser loggedinuser = UMFactory.getLogonAuthenticator().getLoggedInUser();

or

IUser loggedinuser = WDClientUser.getCurrentUser().getSAPUser();

it always hit UWLException: (Default) Logged in users context or session doesn't exist

my code like follows:

	public void getInbox() {
		IWDMessageManager messageManager = wdComponentAPI.getMessageManager();
		wdContext.nodeInboxData().invalidate();
		try {
			IUWLService uwlService = (IUWLService) WDPortalUtils.getServiceReference(IUWLService.ALIAS_KEY);// PortalRuntime.getRuntimeResources().getService(IUWLService.ALIAS_KEY);//
			UWLContext uwlContext = new UWLContext();
			IUser loggedinuser =UMFactory.getLogonAuthenticator().getLoggedInUser(); 
			uwlContext.setAllowBackEndConnections(true);
			uwlContext.setUser(loggedinuser);
			uwlContext.setLocale(loggedinuser.getLocale());
			IUWLSession uwlSession = uwlService.beginSession(uwlContext, 600);
			uwlContext.setSession(uwlSession);
			IUWLItemManager itemManager = uwlService.getItemManager(uwlContext);
			QueryResult result = itemManager.getItemsForItemType(uwlContext, ItemType.UWL_ITEM_NOTIFICATION, null, null);
			ItemCollection coll = result.getItems();
			List l = coll.list();
			Iterator iter = l.iterator();
			while (iter.hasNext()) {
				Item item = (Item) iter.next();
				if (item.getExternalType().equals("UWLNotification") && !item.getStatus().equals(StatusEnum.COMPLETED)) {
					IPrivateMyToDoCompView.IInboxDataElement data = wdContext.nodeInboxData().createInboxDataElement();
					data.setItem(item);
					data.setSubject(item.getSubject());
					data.setDescription(item.getDescription());
					data.setStatus(item.getStatus().getText());
					data.setCreatorId(item.getCreatorId());
					data.setCreatedDate(item.getCreatedDate().toString());
					wdContext.nodeInboxData().addElement(data);
				}
			}
			uwlService.endSession(uwlContext);
		} catch (Exception e) {
			e.printStackTrace();
			messageManager.reportException(" Cause:" + e.getCause() + "\n Message:" + e.getMessage());
		}
	}

can any one tell me why? and i develop with nwce 7.1 ehp1.

thank you