title: error when trying to run a wicket application under eclipse
body: <p>i am trying to build a web application using wicket. but whenever i try to run, i get the following error</p>
  
  <pre><code> SEVERE: StandardWrapper.Throwable java.lang.NoSuchMethodError:
   org.apache.wicket.util.lang.Args.notNull(Ljava/lang/Object;Ljava/lang/String;)V
      at
   org.apache.wicket.request.resource.ResourceReference.&lt;init&gt;(ResourceReference.java:73)
      at
   org.apache.wicket.request.resource.ResourceReference.&lt;init&gt;(ResourceReference.java:89)
      at
   org.apache.wicket.request.resource.PackageResourceReference.&lt;init&gt;(PackageResourceReference.java:69)
      at
   org.apache.wicket.extensions.ajax.markup.html.form.upload.UploadProgressBar.&lt;clinit&gt;(UploadProgressBar.java:110)
      at
   org.apache.wicket.extensions.ajax.markup.html.form.upload.UploadProgressBar$ComponentInitializer.init(UploadProgressBar.java:92)
      at org.apache.wicket.extensions.Initializer.init(Initializer.java:36)
      at
   org.apache.wicket.Application.callInitializers(Application.java:788)
      at
   org.apache.wicket.Application.initializeComponents(Application.java:625)
      at
   org.apache.wicket.protocol.http.WicketFilter.init(WicketFilter.java:575)
      at
   org.apache.wicket.protocol.http.WicketServlet.init(WicketServlet.java:194)
      at javax.servlet.GenericServlet.init(GenericServlet.java:160)   at
   org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1266)
      at
   org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1185)
      at
   org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1080)
      at
   org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:5027)
      at
   org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5314)
      at
   org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
      at
   org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
      at
   org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
      at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
      at java.util.concurrent.FutureTask.run(FutureTask.java:138)     at
   java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
      at
   java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
      at java.lang.Thread.run(Thread.java:619) 
  </code></pre>
  
  <p>Can anybody please explain the reason for the error?</p>