see forum:
https://groups.google.com/forum/embed/?place=forum/camunda-bpm-users&showsearch=true&showpopout=true#!topic/camunda-bpm-users/_bB0wxt4wy0

18.07.2013 18:56:00 org.camunda.bpm.engine.rest.exception.ExceptionHandler toResponse
WARNUNG: java.lang.NullPointerException
at org.camunda.bpm.engine.rest.sub.impl.AbstractVariablesResource.getVariables(AbstractVariablesResource.java:45)
at sun.reflect.GeneratedMethodAccessor259.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:167)
at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:257)
at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:222)
at org.jboss.resteasy.core.ResourceLocator.invokeOnTargetObject(ResourceLocator.java:159)
at org.jboss.resteasy.core.ResourceLocator.invoke(ResourceLocator.java:107)
at org.jboss.resteasy.core.ResourceLocator.invokeOnTargetObject(ResourceLocator.java:154)
at org.jboss.resteasy.core.ResourceLocator.invoke(ResourceLocator.java:92)
at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:542)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:524)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:126)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.camunda.bpm.tasklist.AuthenticationFilter.doFilter(AuthenticationFilter.java:32)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)