issue in google app engine with google cloud sql

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I have made a Google App Engine project in Vaadin with google cloud sql database. I’ve tested it well on my local machine, without (any important) bugs. When I deploy it to GAE it also works for a certain time. Only after x hours it stops working (doing exactly the same as before and without changing anything to the code). If I deploy the project again, it is working again.When I take a look at the GAE logs it seems to be a 2013-03-25 10:26:03.071 com.vaadin.terminal.gwt.server.GAEApplicationServlet service: An exception occurred while servicing request. javax.servlet.ServletException: java.lang.RuntimeException at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.handleServiceException( at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service( at com.vaadin.terminal.gwt.server.GAEApplicationServlet.service( at javax.servlet.http.HttpServlet.service( at org.mortbay.jetty.servlet.ServletHolder.handle( at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(
java google-app-engine vaadin