heiko, can you have a look at this stack trace ?
is that something in the engine or in the console?

22:19:19,546 ERROR [[Resteasy]] Servlet.service() for servlet Resteasy threw exception
org.jboss.resteasy.spi.UnhandledException: java.lang.RuntimeException: Unexpected invocation exception: null
at org.jboss.resteasy.core.SynchronousDispatcher.handleApplicationException(SynchronousDispatcher.java:319)
at org.jboss.resteasy.core.SynchronousDispatcher.handleException(SynchronousDispatcher.java:230)
at org.jboss.resteasy.core.SynchronousDispatcher.handleInvokerException(SynchronousDispatcher.java:206)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:360)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:173)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:93)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:68)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.bpm.console.server.util.GWTJsonFilter.doFilter(GWTJsonFilter.java:59)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:525)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:828)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:601)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.RuntimeException: Unexpected invocation exception: null
at org.jboss.bpm.console.server.util.InvocationProxy.invoke(InvocationProxy.java:80)
at $Proxy140.getProcessImage(Unknown Source)
at org.jboss.bpm.console.server.ProcessMgmtFacade.getProcessImage(ProcessMgmtFacade.java:281)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:117)
at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:260)
at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:232)
at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:166)
at org.jboss.resteasy.core.DispatcherUtilities.getJaxrsResponse(DispatcherUtilities.java:142)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:356)
... 28 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.bpm.console.server.util.InvocationProxy.invoke(InvocationProxy.java:64)
... 40 more
Caused by: java.lang.RuntimeException: Failed to retrieve image resource: null
at org.jbpm.integration.console.graphView.GraphViewerPluginImpl.getProcessImage(GraphViewerPluginImpl.java:77)
... 45 more