Pb java.lang.NoClassDefFoundError erreur java

Bonjour,
Quelq'un sait-t-il que est ce que ça veut dire l'erreur suivante :
Code:
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Initializing AppEngine server
[WARN] No file found for: /favicon.ico
[WARN] No file found for: /favicon.ico
[WARN] No file found for: /favicon.ico
[WARN] No file found for: /favicon.ico
[WARN] Error for /gwtfileupload/upload
java.lang.NoClassDefFoundError: fr/tlse/valtech/progres/model/ValtechUser
	at com.hsn.demo.gwtfileupload.server.ReadStreamService.read(ReadStreamService.java:31)
	at com.hsn.demo.gwtfileupload.server.FileUploadServlet.doPost(FileUploadServlet.java:42)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
	at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:58)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
	at com.google.apphosting.utils.jetty.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:70)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:349)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.Server.handle(Server.java:326)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
	at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
	at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
	at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
	at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: java.lang.ClassNotFoundException: fr.tlse.valtech.progres.model.ValtechUser
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:151)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 29 more
[WARN] No file found for: /favicon.ico
merci d'avance