title: Tabris UICallback Exception
body: <p>i want to aktivate the UICallback in tabris on my iPad but when i call <code>UICallback.aktivate("background")</code> after each display opperation an IllegalArgumentException is thrown:</p>
  
  <pre><code>2012-10-04 11:57:53.424:WARN:oejs.ServletHandler:ERROR:  /dashboard;jsessionid=26uqw2kydt3v4ehzfgj2wgo9
  java.lang.IllegalArgumentException: No service handler registered with id org.eclipse.rwt.internal.uicallback.UICallBackServiceHandler
      at org.eclipse.rap.rwt.internal.service.ServiceManager.getCustomHandlerChecked(ServiceManager.java:58)
      at org.eclipse.rap.rwt.internal.service.ServiceManager.getHandler(ServiceManager.java:48)
      at org.eclipse.rap.rwt.engine.RWTServlet.handleValidRequest(RWTServlet.java:101)
      at org.eclipse.rap.rwt.engine.RWTServlet.doPost(RWTServlet.java:80)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:755)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
      at org.eclipse.rap.rwt.osgi.internal.CutOffContextPathWrapper.service(CutOffContextPathWrapper.java:106)
      at org.eclipse.equinox.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:61)
      at org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:128)
      at org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:60)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
      at org.eclipse.equinox.http.jetty.internal.HttpServerManager$InternalHttpServiceServlet.service(HttpServerManager.java:384)
      at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:598)
      at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:486)
      at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
      at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1065)
      at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:413)
      at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:192)
      at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:999)
      at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
      at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:111)
      at org.eclipse.jetty.server.Server.handle(Server.java:350)
      at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:454)
      at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:900)
      at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:954)
      at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:851)
      at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
      at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:77)
      at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:606)
      at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:46)
      at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:603)
      at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:538)
      at java.lang.Thread.run(Unknown Source)
  </code></pre>
  
  <p>I'm using the com.eclipsesource.tabris.feature.feature.group 0.7.0.v20120828-1253</p>
  
  <p>I have also tested the Train Dashboard Demo from <a href="http://developer.eclipsesource.com/tabris/demos/" rel="nofollow">http://developer.eclipsesource.com/tabris/demos/</a> it accurs the same Problem but in the screencast it looks like it worked in the past...</p>
  
  <p>Thanks for help</p>