Cannot shutdown managed server

Please help.

I am trying to shutdown a managed server that is in unknown state. Tried through admin console and stopManagedweblogic.sh. Getting following error:

weblogic.utils.AssertionError: ***** ASSERTION FAILED *****

        at weblogic.server.ServerLifeCycleRuntime.getStateRemote(ServerLifeCycleRuntime.java:734)

        at weblogic.server.ServerLifeCycleRuntime.getState(ServerLifeCycleRuntime.java:581)

        at weblogic.server.ServerLifeCycleRuntime.shutdown(ServerLifeCycleRuntime.java:432)

        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:597)

        at weblogic.management.jmx.modelmbean.WLSModelMBean.invoke(WLSModelMBean.java:437)

        at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:836)

        at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:761)