NullPointerException happened in using pushBackTask operation ????????????

Question

Hi,
I put an invoke activity into the bpel process to invoke pushBackTask operation in TaskService. But the process got a "java.lang.NullPointerException" when execute this activity. While it had no detail information.
Then open the audit the process information in BPELConsole, it show the detail xml information like this. Is there anybody knowhow to fix this. Thanks.
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<messages><input><pushBackTaskMessage><part xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="payload"><pushBackTask xmlns="http://xmlns.oracle.com/bpel/workflow/taskService">
<workflowContext xmlns="http://xmlns.oracle.com/bpel/workflow/common">
<credential>
<login>bpeladmin</login>
<identityContext>jazn.com</identityContext>
</credential>
<token>pyHGQ7NkSxOTA0/rz9FLwmsi3+1yW/LiS7eTYY3zOv6XyVW1gi2/mU5EJHVWOfalVL1koQYczeHlUE3fl4yvA9GAsezTFonLuQtb84khaEJpaOUFsBflwg1c5n7J/JE37eJW6HeqoT2utGTwWCfWP3Pm9InF5TUTVe2fymzwB4KV1x/wj6I7NxacZA61zELke1Pf+7vsbf1dzwvhx+TZygROIwwdtEI+6xdqp0ULztLLucadYKHcjUaVZzWTW2jrOogcTxbQfk8=</token>
</workflowContext>
<task xmlns="http://xmlns.oracle.com/bpel/workflow/task">
<title>填写请假单</title>
<payload xmlns="http://xmlns.oracle.com/bpel/workflow/task">
<ApplyTitle>w</ApplyTitle>
<ApplyUserName>jcooper</ApplyUserName>
</payload>
<taskDefinitionURI>http://FOX000:80/orabpel/default/VacationApplyProcess2/1.1/HumanTask_Apply/HumanTask_Apply.task</taskDefinitionURI>
<ownerUser>bpeladmin</ownerUser>
<priority>3</priority>
<identityContext>jazn.com</identityContext>
<processInfo>
<domainId>default</domainId>
<instanceId>140004</instanceId>
<processId>VacationApplyProcess2</processId>
<processName>VacationApplyProcess2</processName>
<processType>BPEL</processType>
<processVersion>1.1</processVersion>
</processInfo>
<systemAttributes>
<approvalDuration>20911</approvalDuration>
<assignedDate>2008-06-19T23:35:05+08:00</assignedDate>
<assigneeUsers>
<id>jcooper</id>
<displayName></displayName>
</assigneeUsers>
<createdDate>2008-06-19T23:35:05+08:00</createdDate>
<digitalSignatureRequired>false</digitalSignatureRequired>
<endDate>2008-06-19T23:35:25.911+08:00</endDate>
<hasSubTasks>false</hasSubTasks>
<inShortHistory>true</inShortHistory>
<isGroup>false</isGroup>
<numberOfTimesModified>3</numberOfTimesModified>
<outcome>APPROVE</outcome>
<passwordRequiredOnUpdate>false</passwordRequiredOnUpdate>
<pushbackSequence>-1-3</pushbackSequence>
<secureNotifications>false</secureNotifications>
<state>COMPLETED</state>
<taskId>7acb33134829849a:743117a4:11aa1437ced:-7ae6</taskId>
<taskNumber>10226</taskNumber>
<updatedBy>
<id>jcooper</id>
</updatedBy>
<updatedDate>2008-06-19T23:35:25.911+08:00</updatedDate>
<version>3</version>
<versionReason>TASK_VERSION_REASON_COMPLETED</versionReason>
<taskDefinitionId>default_VacationApplyProcess2_1.1_HumanTask_Apply</taskDefinitionId>
<taskDefinitionName>HumanTask_Apply</taskDefinitionName>
</systemAttributes>
<systemMessageAttributes/>
<callback/>
</task>
<taskId/>
</pushBackTask>
</part></pushBackTaskMessage></input><fault><operationErroredFault xmlns="http://xmlns.oracle.com/bpel/workflow/taskService"><part name="payload"><operationErroredFault xmlns="http://xmlns.oracle.com/bpel/workflow/taskService">
<faultInfo>java.lang.NullPointerException</faultInfo>
</operationErroredFault>
</part></operationErroredFault></fault></messages>
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Answer 1

Same error here....
can someone please help!!!
Thanks,
Deepti