I'm using the same sample and using the most current version of the SDK (11.2) and I still get the same error.  "An item with the same key has already been added."  I'm trying to open the top level.  This was working when I had both foreach loops in the event and had returns after the assignment to true, but I don't see why that would work.  Does this mean I have to keep track of when I toggle the cell open rather than just check the flag that should be set?

private void ExpandTopLevelCell(IEnumerable<PivotHeaderCell> cells)

{

       foreach (PivotHeaderCell cell in cells)

       {

              // The top level cell has NO PARENT.

              if (cell.ParentCell == null && cell.IsToggleVisible && cell.IsExpanded == false)

              {

                     cell.IsExpanded = true;

              }

       }

}

private void uxMainPivotGrid_LayoutLoaded(object sender, EventArgs e)

{

       ExpandTopLevelCell(uxMainPivotGrid.GridLayout.ColumnHeaderCells);

       ExpandTopLevelCell(uxMainPivotGrid.GridLayout.RowHeaderCells);

}