Debugging template/workitem issues

Hi
We have made several changes to the Work Item template in our project. At some stage we stopped being able to view work items through the Eclipse UI. The Eclipse log shows:

!ENTRY com.ibm.team.workitem.ide.ui 4 2 2014-03-27 10:22:15.114
!MESSAGE Problems occurred when invoking code from plug-in: "com.ibm.team.workitem.ide.ui".
!STACK 0
org.eclipse.core.runtime.AssertionFailedException: assertion failed:
        at org.eclipse.core.runtime.Assert.isTrue(Assert.java:110)
        at org.eclipse.core.runtime.Assert.isTrue(Assert.java:96)
        at com.ibm.team.workitem.common.model.ItemProfile.contains(ItemProfile.java:316)
        at com.ibm.team.workitem.client.internal.util.AuditableBatchResolver.add(AuditableBatchResolver.java:60)
        at com.ibm.team.workitem.client.internal.util.ResolvedWorkItem.add(ResolvedWorkItem.java:365)
        at com.ibm.team.workitem.client.internal.util.ResolvedWorkItem.collect(ResolvedWorkItem.java:291)
        at com.ibm.team.workitem.client.internal.util.ResolvedWorkItem.resolve(ResolvedWorkItem.java:253)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemUIWorkingCopy.resolve(WorkItemUIWorkingCopy.java:231)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInput.resolveAuxiliaryItems(WorkItemEditorInput.java:254)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInput.access$4(WorkItemEditorInput.java:244)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInput$1.run(WorkItemEditorInput.java:180)
        at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInput.fetchAll(WorkItemEditorInput.java:153)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInput.getWorkingCopy(WorkItemEditorInput.java:126)
        at com.ibm.team.workitem.ide.ui.internal.editor.WorkItemEditorInputFuture$1.runProtected(WorkItemEditorInputFuture.java:86)
        at com.ibm.team.foundation.client.util.FoundationJob.run(FoundationJob.java:68)
        at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)

We cannot revert the template because ( I think this the fields that have been changed/added are in use) and now RTC is really unusable for our development team.

The changes were made in RTC level 4.0.2 and 4.0.3. The server has just been upgraded to 4.0.6 which has not fixed the issue.

Any guidance on how we might debug this (and fix!) this would be very much appreciated.