V7.2.1 Umbraco Core Property Value Converters (UCPVC) installed

I know this is to do with Archetype but there's no problem if I don't have UCPVC installed. So........

I have an Archetype field set which I can get an image from a Media Picker ok but am unable to retreive a simple textbox value.  I know that when I haven't had UCPVC installed, in the following code, to get the H4 I'd just use fieldset.GetValue("subSectionTitle"). I'm afraid I can't work out how to get to it with the UCPVC installed.

Code:-

@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@using Archetype.Models;
@using Archetype.Extensions;
@{
    var subSections = Model.Content.GetPropertyValue<ArchetypeModel>("pageSections");
}
<div>
  <ul>
        @{int counter = 1;}
        @foreach(var fieldset in subSections){  
        var icon = Umbraco.TypedMedia(fieldset.GetValue("icon"));
        <li>
            <div>
                <a href="#tabs-@counter" title="@icon.Name"><img src="@icon.GetResponsiveCropUrl("SupportIcon")" alt="@icon.Name"></a>
                <h4>@fieldset.GetProperty("subSectionTitle").Value.ToString()</h4>
            </div>
        </li>
        counter++;
        }
    </ul>
</div>

Result:-

Compiler Error Message: CS1061: 'Archetype.Models.ArchetypeFieldsetModel' does not contain a definition for 'GetProperty' and no extension method 'GetProperty' accepting a first argument of type 'Archetype.Models.ArchetypeFieldsetModel' could be found (are you missing a using directive or an assembly reference?)

Have tried several ways but no luck.

Any clue would be appreciated.

Thanks,

Craig