Vaadin and Google AppEngine project error.

I followed the next instructions:
Create a new Vaadin project as described in the Book of Vaadin
Select “Google App Engine servlet” as deployment type.
Select to use Vaadin version 6.3.0 or newer. click “Download…” if it is not in the list.
Enable GAE
In project preferences check “Use Google App Engine” in Google/App Engine.
Click the “My applications…” link
Log into your Google App Engine account
Create a new web application in “My Applications” list
Add created the application id to your project configuration in Eclipse
Code and configure your application.
Deploy to App Engine by clicking the project with right mouse button and selecting Google/Deploy to App Engine, or click the “Deploy to App Engine” icon in the toolbar.
Run the application in

Note! There is a problem in the latest GAE plugin which prevents this from working. If you get an error like “The App Engine SDK ‘C:<workspace path><project name>\war’ on the project’s build path is not valid” do the following:

Open preferences -> Google -> App Engine and select the sdk version again
Open prefercense -> Java Build Path -> Export Order. Change the Export order so that the App Engine SDK is ABOVE the "Web App Libraries" classpath container. 


and the project is not with errors,
but I get the error log in eclipse when I run the project:

and Eclipse say:[quote]
Critical error I’m sorry, but there seems to be a serious problem, please contact the administrator. And please take note of any unsaved data…

Yesterday, Vaadin 6.7.4.jar worked fine !!!

OK I read the next notes:

and I changed it in web.xml

Vaadin_gwt Application


It works fine !!!

Thank you,
Mauro M.E