I attached a sample project, without the ig_res folder. I am using version 10.2. To reproduce the issue, you can edit a value in the grid and click the "Test" button.

The original problem we needed to solve was to display sums of values (subtotals) for several rows in the grid. That's why we started using the WebHierarchicalDataGrid (WHDG). We managed to display the sum of cell values from the rows in the child band in the parent row when initially loading the grid, but when trying to edit values and post back, we get exceptions like the one below. The message "Property Year1Cost not found" probably refers to the name of the property Year1Cost in the object GroupedComponent, list of which we bind to the grid. Please let us know if using WHDG is the right way to get subtotals. If it is the right way, can you let us know how to use the grid properly so as to avoid the exception and be able to edit and save the values from the grid. Thank you.

System.Exception was unhandled by user code
  Message="Property Year1Cost not found."
  Source="Infragistics35.Web.v10.2"
  StackTrace:
       at Infragistics.Web.UI.Framework.Data.EnumerableDataSourceAdapter.Update(Object dataItem, IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\Framework\Data\DataAdapters.cs:line 165
       at Infragistics.Web.UI.Framework.Data.DataSourceObjectView.Update(Object dataItem, IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\Framework\Data\DataSourceObjectView.cs:line 301
       at Infragistics.Web.UI.GridControls.EditingCore.OnAction(String actionType, Object id, Object value, Object tag) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebDataGrid\Behaviors\Editing\EditingCore.cs:line 368
       at Infragistics.Web.UI.GridControls.GridBehavior.Infragistics.Web.UI.GridControls.IGridBehavior.OnAction(String actionType, Object id, Object value, Object tag) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebDataGrid\Behaviors\GridBehavior.cs:line 586
       at Infragistics.Web.UI.GridControls.GridBot.LoadAdditionalClientState(Object state) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebDataGrid\GridBot.cs:line 544
       at Infragistics.Web.UI.GridControls.ContainerGridBot.LoadAdditionalClientState(Object state) in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebHierarchicalDataGrid\ContainerGridBot.cs:line 288
       at Infragistics.Web.UI.Framework.RunBot.HandleRaisePostDataChangedEvent() in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\Framework\RunBot.cs:line 599
       at Infragistics.Web.UI.GridControls.GridBot.HandleRaisePostDataChangedEvent() in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebDataGrid\GridBot.cs:line 565
       at Infragistics.Web.UI.GridControls.ContainerGrid.RaisePostDataChangedEvent() in e:\Work\2\161\Sources\RELEASE\ASP.NET\2010.2\Source\Infragistics.Web.UI\GridControls\WebHierarchicalDataGrid\ContainerGrid.cs:line 2080
       at System.Web.UI.Page.RaiseChangedEvents()
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
  InnerException: