NPE Opening Work Item

I'm getting the following when trying to open a work item. I'm using com.ibm.team.workitem.editor.default as the editor to use.

This is a relatively new project - I created this morning based on Simple Team Process and have been modifying. I added some roles, modified some permissions. Added a new tab to the Work Item page, but later removed it.

Any thoughts?

Thanks, Gary

An error has occurred. See error log for more details.
java.lang.NullPointerException

The log has:
!ENTRY org.eclipse.jface 4 2 2008-12-17 11:20:37.421
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.jface".
!STACK 0
java.lang.NullPointerException
at com.ibm.team.workitem.rcp.ui.WorkItemUI.openEditor(Unknown Source)
at com.ibm.team.workitem.rcp.ui.internal.explorer.view.AbstractWorkItemExplorer.openSelection(Unknown Source)
at com.ibm.team.workitem.rcp.ui.internal.explorer.view.AbstractWorkItemExplorer$7.open(Unknown Source)