Set up grouping for xamgrid in xaml:

<ig:XamGrid.GroupBySettings>
        <ig:GroupBySettings AllowGroupByArea="Top" />
    </ig:XamGrid.GroupBySettings>

then run the app and try to drap and drop column header to group area, very often, got following error:

unable to cast object of type 'Infrigistics.Controls.Grids.Row' to type 'Infrisgistics.Controls.Primitives.GroupByRow'.
 at Infragistics.Controls.Grids.XamGrid.WalkDownGroupByRowsForDataItem(RowCollection rows, Object data)
   at Infragistics.Controls.Grids.XamGrid.ActiveItemChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.RaisePropertyChangeNotifications(DependencyProperty dp, Object oldValue, Object newValue)
   at System.Windows.DependencyObject.UpdateEffectiveValue(DependencyProperty property, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, ValueOperation operation)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet)
   at Infragistics.Controls.Grids.XamGridRowsManager.OnCurrentItemChanged(Object data)
   at Infragistics.Controls.Grids.RowsManager.DataManager_CurrentItemChanged(Object sender, CurrentItemEventArgs e)
   at Infragistics.DataManagerBase.OnCurrentItemChanged(Object item)
   at Infragistics.DataManagerBase.ICollectionViewData_CurrentChanged(Object sender, EventArgs e)
   at System.Windows.Data.PagedCollectionView.OnCurrentChanged()
   at System.Windows.Data.PagedCollectionView.RaiseCurrencyChanges(Boolean fireChangedEvent, Object oldCurrentItem, Int32 oldCurrentPosition, Boolean oldIsCurrentBeforeFirst, Boolean oldIsCurrentAfterLast)
   at System.Windows.Data.PagedCollectionView.RefreshOverride()
   at System.Windows.Data.PagedCollectionView.Refresh()
   at System.Windows.Data.PagedCollectionView.EndDefer()
   at System.Windows.Data.PagedCollectionView.DeferHelper.Dispose()
   at Infragistics.DataManager`1.ResolveFilteredSortedPagedDataSource()
   at Infragistics.DataManagerBase.InvalidateSortedFilterdDataSource()
   at Infragistics.DataManagerBase.ClearCachedDataSource(Boolean invalidateTotalRowCount)
   at Infragistics.DataManager`1.ClearCachedDataSource(Boolean invalidateTotalRowCount)
   at Infragistics.Controls.Grids.RowsManager.InvalidateSort()
   at Infragistics.Controls.Grids.RowsManager.InvalidateGroupBy(Boolean reset)
   at Infragistics.Controls.Grids.XamGridRowsManager.InvalidateGroupBy(Boolean reset)
   at Infragistics.Controls.Grids.RowsManager.OnColumnLayoutPropertyChanged(ColumnLayout layout, String propertyName)
   at Infragistics.Controls.Grids.XamGridRowsManager.OnColumnLayoutPropertyChanged(ColumnLayout layout, String propertyName)
   at Infragistics.Controls.Grids.RowsManagerBase.OnColumnLayoutPropertyChanged(Object sender, PropertyChangedEventArgs e)
   at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e)
   at Infragistics.DependencyObjectNotifier.OnPropertyChanged(String propertyName)
   at Infragistics.Controls.Grids.ColumnLayout.InvalidateGroupBy()
   at Infragistics.Controls.Grids.GroupByColumnsCollection.OnGroupingChanged(IList`1 oldCollection, IList`1 newCollection)
   at Infragistics.Controls.Grids.GroupByColumnsCollection.AddItem(Int32 index, Column item)
   at Infragistics.Collections.CollectionBase`1.Add(T item)
   at Infragistics.Controls.Grids.Column.set_IsGroupBy(Boolean value)
   at Infragistics.Controls.Grids.Primitives.HeaderCellControl.OnMouseLeftButtonUpColumnMoving(MouseButtonEventArgs e)
   at Infragistics.Controls.Grids.Primitives.CellControlBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
   at System.Windows.Controls.Control.OnMouseLeftButtonUp(Control ctrl, EventArgs e)
   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventNam

how to resolve this problem.