Shipping Director provides ability for the calculation of an Error Description using the Error (or ErrorExit) record type. But, out of the box, nopC will not show the HTML correctly. One needs to just modify the view file - e.g.
\Views\ShoppingCart\EstimateShipping.cshtml@foreach (var error in Model.Warnings)
{
<li>@error</li>
}
@foreach (var error in Model.Warnings)
{
<li>@Html.Raw(error)</li>
}