Automatic survey email not working

We have configured our ServiceDesk MSP installation to send out survey emails whenever a request is closed.

When a request in a "Resolved" stated ages (7 days in our system) and closes, there is a Null Pointer Exception in the logs, and no survey email is sent.

[12:47:52:316]|[09-12-2011]|[com.adventnet.servicedesk.utils.ServiceDeskUtil]|[SEVERE]|[41]|: Exception while getting user credentials in getUserId. Assuming Non-Login view. |
[12:47:52:316]|[09-12-2011]|[com.adventnet.servicedesk.utils.WorkOrderUtil]|[SEVERE]|[41]|: WorkOrderUtil >> closeRequest >> Exception occured while closing the request |java.lang.NullPointerException
        at com.adventnet.servicedesk.utils.WorkOrderUtil.closeRequest(WorkOrderUtil.java:7698)
        at com.adventnet.servicedesk.utils.WorkOrderUtil.closeRequest(WorkOrderUtil.java:7588)
        at com.adventnet.servicedesk.utils.WorkOrderUtil.checkAgedRequests(WorkOrderUtil.java:7326)
        at com.adventnet.servicedesk.task.RequestAgingTask.executeTask(RequestAgingTask.java:31)
        at com.adventnet.workengine.task.internal.TaskManagerImpl.executeTask(TaskManagerImpl.java:706)
        at com.adventnet.workengine.executor.internal.WorkFlowExecutor.executeStartingTask(WorkFlowExecutor.java:160)
        at com.adventnet.workengine.executor.internal.WorkFlowExecutor.executeWorkFlowTemplate(WorkFlowExecutor.java:115)
        at com.adventnet.workengine.executor.internal.WorkFlowExecutor.executeWorkFlow(WorkFlowExecutor.java:105)
        at com.adventnet.workengine.workflow.ejb.internal.WorkFlowExecutorBean.executeWorkFlow(WorkFlowExecutorBean.java:105)
        at sun.reflect.GeneratedMethodAccessor153.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

(... continues..)

Closing a request manually works correctly.

Our server runs on CentOS 5.5 with OpenJDK 1.6.0_17.

Has anyone else experienced this?

I've Cc'd Support into this as well...

Cheers

Stuart