Process engine not able to submit document to Beoker in WM 7.0 with IS 65 SP3

Hi Gurus,
I am using WM 7.0 with IS SP3 and broker 6.5
-When executing a process, I am getting the following errors when ever PRT is submitiing a document to Broker.Struglling to overcome this error form quite a number of days
1.Business process having HumanTask
2.Referenced process
3.Whneever process status is changed

  • *** Error sending wm.prt.dispatch:ProcessTransitionVol:
  • *** Error sending wm.prt.status:ChangeCommandVol:
    2009-10-28 15:06:33 IST [PRT.0101.0003V4] com.wm.app.prt.ProcessException: [PRT.0101.9130] Error sending wm.prt.status:ChangeCommandVol: >>>BasicData:ProcessInstanceID=5fe38520c3a511de9389bb8214bf4780,ProcessModelID=DocProcess/addmath,ProcessModelVersion=1,ProcessIteration=1,Action=FAIL,CorID=9A80EE729B230DD001135D348A753FA9,1:1:1,0,1,mokap01-xp2|UnknownProcess|UnnamedAgent|WebMethods|Flow Services|Math|doctryadd,20,H4sIAAAAAAAAAE2N206DQBCGEa2H1kMbX8AXkMAuB7kEscELExPphZeTdoNYGDYsah/f7YyJvZiZ5P++ye86ztF7mTv2LPfLzuITvsH7GpvWK8F8vIC24YQcd++4dubktIC19zYODdbOItPaqo/QtmrIaoUjfRw/0cflChE6tfkHJwym1Q6rAdbqeUPxhOO7NIvyZRqLNBfSLwrfDwIZFTIMpYiTB1mQfMry/LC67A0XnDGcdf0WtB/c77Sg/JzzG9arplNmhE4Tu2B2FYgoToSIUhknIZEpk9vDqtehXytjiM+YX69wi/0P/qFf3KqztV4BAAA=<<<
    java.lang.NullPointerException
    at com.wm.app.b2b.server.InvokeState.clone(InvokeState.java:205)
    at com.wm.app.b2b.server.ServiceThread.(ServiceThread.java:35)
    at com.wm.app.b2b.server.Service.doThreadInvoke(Service.java:851)
    at com.wm.app.prt.transport.TransportManager.invoke(TransportManager.java:167)
    at com.wm.app.prt.transport.Transport_BROKER.send(Transport_BROKER.java:32)

Any pointers for root cause of this problem would be a great help?

Thanks in Advance,
Aparna