Thank you for the sample, we could replicate the issue in our environment. A bug report has been submitted for this issue.

We will inform you if there is any update or progress regarding this issue.

The fix discussed in this thread is for composite key scenario. In your case, since you are only using 1 datakeyfield this fix probably will not solve the issue.

Could you supply us with a screenshot of the error message or a running sample so we could try to replicate the scenario in our environment. If the sample is not possible perhaps you could detailed the steps require to replicate the issue.

Based on the analysis of our developer, this issue is not caused by a bug. In order to solve this issue, you will need to set the DataKeyField of the WebGrid RootTable after you invoke the RetrieveStructure function.

In the attached sample,  that would be in the PrepareDataBinding event handler. Here is the modified snippet in the PrepareDataBinding event handler:

protected void WebGrid1_PrepareDataBinding(object sender, ISNet.WebUI.WebGrid.DataSourceEventArgs e)
{

    // make sure retrievestructure is only called when the RefreshAll() is invoked from client or when the first time page load.
    if (WebGrid1.FlyPostBackAction == PostBackAction.RefreshAll || !IsPostBack)
    {
        // clear all grouped and sorted columns since that they are no longer exist in new datasource's structure.
        WebGrid1.RootTable.SortedColumns.Clear();
        WebGrid1.RootTable.GroupedColumns.Clear();

        // populates columns
        WebGrid1.RetrieveStructure();

        WebGrid1.RootTable.Columns.GetNamedItem("OrderID").EditType = EditType.NoEdit;
        WebGrid1.RootTable.Columns.GetNamedItem("OrderID").FilterEditType = FilterEditType.TextBox;
        WebGrid1.RootTable.Columns.GetNamedItem("OrderID").AggregateFunction = AggregateFunctions.Count;
        WebGrid1.RootTable.Columns.GetNamedItem("OrderID").FooterText = "Total:"; 

        WebGrid1.RootTable.Columns.GetNamedItem("CustomerID").EditType = EditType.DropdownList;
        WebGrid1.RootTable.Columns.GetNamedItem("CustomerID").FilterEditType = FilterEditType.DropdownList;

        WebGrid1.RootTable.Columns.GetNamedItem("EmployeeID").EditType = EditType.WebComboNET;
        WebGrid1.RootTable.Columns.GetNamedItem("EmployeeID").FilterEditType = FilterEditType.WebComboNET;
        WebGrid1.RootTable.Columns.GetNamedItem("EmployeeID").WebComboID = WebCombo1.ID;

        WebGrid1.RootTable.DataKeyField = "OrderID";
    }

    //Set the valueList for the Customer
    WebValueList vlAssetType = WebGrid1.RootTable.Columns.GetNamedItem("CustomerID").ValueList;
    vlAssetType.DataSource = GetCustomers();
    vlAssetType.DataValueField = "CustomerID";
    vlAssetType.DataTextField = "CompanyName";

    ////Set the valueList for the Employee
    WebValueList vlWSCSecType = WebGrid1.RootTable.Columns.GetNamedItem("EmployeeID").ValueList;
    vlWSCSecType.DataSource = GetEmployees();
    vlWSCSecType.DataValueField = "EmployeeID";
    vlWSCSecType.DataTextField = "LastName";

}