When attempting to change edit mode for a telerik grid to anything other than 'InLine' I get an error about passing in the wrong model type

[Ahmed]

I create the grid like so:

Html.Telerik().Grid<myapp.Date>("dates")
    .Name("MyGrid")
    .Pageable(paging => paging.PageSize(10))
    .Sortable()
    .Filterable()
    .Groupable()
    .DataKeys(keys => keys.Add(c => c.id))
    .DataBinding(dataBinding =>
    {
        dataBinding.Ajax()
        .Select("_SelectAjaxEditing", "Dates")
        .Insert("_InsertAjaxEditing", "Dates")
        .Update("_SaveAjaxEditing", "Dates")
        .Delete("_DeleteAjaxEditing", "Dates");
    })
    .ToolBar(commands => commands.Insert())
    .Columns(columns =>
    {
        columns.Bound(o => o.name);
        columns.Bound(o => o.date1);
        columns.Command(commands =>
        {
            commands.Edit().ButtonType(GridButtonType.Text);
            commands.Delete().ButtonType(GridButtonType.Text);
        });
    })
    .Editable(editing => editing.Mode(GridEditMode.InLine))
    .Render();
    %>

and it runs fine, but if I change the GridEditMode to be anything other than InLine I get the following error:

The model item passed into the dictionary is of type 'myapp.Date', but this dictionary requires a model item of type 'System.Nullable`1[System.DateTime]'.

There is a system.DateTime field in the grid, is that the reason for this error?