Ghost Local Connection cannot be deleted in PowerPivot

In PowerPivot (add in for MS Excel 2010), I have a Local Connection (*.odc) which cannot be deleted.  For other connections, whenI click on the connection, I have an option to delete.  However, for the item under the Local Connections heading, which I click on it, the delete button remains greyed out.  I'm not aware that this local connection is being used in the workbook.  How do I delete it?!