HTTP Status 500

what could be the problem when the console displays

javax.servlet.ServletException: Failed to load application class: com.example.myproject.MyprojectUI
com.vaadin.terminal.gwt.server.ApplicationServlet.init(ApplicationServlet.java:71)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:307)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
java.lang.Thread.run(Thread.java:679)

Whenever I try to run the project.

No changes to the web.xml file created by the project

My IDE is Eclipse Juno, Vaadin 6.8.6 running on Linux ubuntu.

Hi Joseph
Have you tried to delete Tomcat in Eclipse and redeploy your application in a new one ?

Thank you Gebel for the reply, I have done it several times but without success, I also tried the J2EE Preview run time without success, I have tomcat is installed in /opt/tomcat directory. I have downloaded some war files like sample.war and it works without problems in the tomcat webapps, I have tried to export the war file from the “Hellow vaadin user” provided on any vaadin project you create still I get the same errors.

Can you post an archive of your project please ?