Specified argument was out of the range of valid values

I have one dropdownbox(ddlCountryTax) containing allcountries,If i select USA it will display grid displaying Tax information related to USA.If i edit information in grid and if we change country USA to UK in dropdown box in the ddlCountryTax(not the dropdownbox coming in the edit window of grid,,no problem for that) it displaying error like

Specified argument was out of the range of valid values. Parameter name: ItemHierarchicalIndex Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values. Parameter name: ItemHierarchicalIndex

Source Error:

Line 86: } Line 87: Line 88: if( rgStateTax.EditItems.Count > 0 ) Line 89: { Line 90: foreach( GridDataItem item in rgStateTax.Items )

Source File: c:\Projects\ACS\Aivea.Acs.Administration\UserControls\TaxManager.ascx.cs Line: 88

Stack Trace:

[ArgumentOutOfRangeException: Specified argument was out of the range of valid values. Parameter name: ItemHierarchicalIndex] Telerik.WebControls.GridItemCollection.get_Item(String hierarchicalIndex) +323 Telerik.WebControls.GridDataItemCollection.get_Item(String hierarchicalIndex) +37 Telerik.WebControls.RadGrid.get_EditItems() +215 Aivea.Acs.Administration.TaxManager.rgStateTax_PreRender(Object sender, EventArgs e) in c:\Projects\ACS\Aivea.Acs.Administration\UserControls\TaxManager.ascx.cs:88 System.Web.UI.Control.OnPreRender(EventArgs e) +8682870 System.Web.UI.WebControls.BaseDataBoundControl.OnPreRender(EventArgs e) +31 Telerik.RadGridUtils.RadControl.OnPreRender(EventArgs e) +36 Telerik.RadGridUtils.RadAJAXControl.OnPreRender(EventArgs e) +37 Telerik.WebControls.RadGrid.OnPreRender(EventArgs e) +40 System.Web.UI.Control.PreRenderRecursiveInternal() +80 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Control.PreRenderRecursiveInternal() +171 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +842

this is code dropdown event

Code:

---

              protected void ddlCountryTax_SelectedIndexChanged( object sender, EventArgs e )
        {
            long locationId = ddlCountryTax.SelectedItem.Value.AsLong();

            ContentAdministrationServiceClient client = null;
            List<DCTaxRate> taxRate = null;
            try
            {
                client = new ContentAdministrationServiceClient();
                taxRate = client.GetTaxRatesByCountryIdAndLocationTypeName( locationId, "State" );
                client.Close();
            }
            catch( FaultException )
            {
                AbortClient( client );
            }

            rgStateTax.DataSource = taxRate;
            rgStateTax.Rebind();

        }

---

this is radgrid

Code:

---

protected void rgStateTax_EditCommand( object sender, EventArgs e )
        {
            BindStateTax();
        }

---

Code:

---

private void BindStateTax()
        {
            long locationId = ddlCountryTax.SelectedItem.Value.AsLong();

            List<DCTaxRate> taxRate = null;
            ContentAdministrationServiceClient client = null;
            try
            {
                client = new ContentAdministrationServiceClient();
                taxRate = client.GetTaxRatesByCountryId( locationId );
                client.Close();
            }
            catch( FaultException )
            {
                AbortClient( client );
            }

            rgStateTax.DataSource = taxRate;
            rgStateTax.Rebind();
        }





  if( ddlState.SelectedIndex > 0 )
            {
                txtState.Text = ddlState.SelectedItem.Text;
            }
            taxRate.StateName = txtState.Text;

---

If you step the code, what line throws the error