GAE Issue

My application works fine on the local development server, but when I upload it to google app engine it keeps getting an error and does not start at all.

If I use VaadinServlet instead on GAEVaadinServlet in web.xml; the application starts fine, but can’t handle clicks or something else. There is always a “Communication Error”.

Here are my files:

Here the error I receive:

This happens when I replace GAEVaadinServlet with VaadinServlet in web.xml (on every button click):

Please help, I don’t know what to do any more …