Required Error Message is not displaying as expected on a field that is a Dropdown List

I have the following metadata for my model (just showing the one data table):

public class AppCatalog_DatabaseMetadata
    {
        [UIHint("MVC4PrimaryKey")]
        [DisplayName("ID")]
        public int databaseID { get; set; }
        [HtmlProperties(Size = 100, MaxLength = 100)]
        [Required(ErrorMessage = "* Database Name is required")]
        [DisplayName("Database Name")]
        [UIHint("MVC4String")]
        public string databaseName { get; set; }
        [DisplayName("Description")]
        [UIHint("MVC4TextBox")]
        [HtmlProperties(Rows = 5, Cols = 75, MaxLength = 1000)]
        [Required(ErrorMessage = "* Description is required")]
        public string databaseDescription { get; set; }
        [DisplayName("S1")]
        [UIHint("ServerType")]
        [Required(ErrorMessage = "* Server Type is required")]
        public int databaseServerTypeID { get; set; }
        public virtual AppCatalog_ServerType AppCatalog_ServerType { get; set; }
    }

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I am using the built-in [Required] attribute.

Here are my Create actions in my controller:

        public ViewResult Create()
        {
            ViewBag.Title = "Application Catalog -> Database Catalog -> Add Database";
            SelectList slServerType = new SelectList(db.AppCatalog_ServerType, "servertypeID", "servertypeName");
            ViewBag.databaseServerTypeID = slServerType;
            return View();
        }

        //
        // POST: /DBCatalog/Create

        [HttpPost]
        public ActionResult Create(AppCatalog_Database appcatalog_database)
        {
            if (ModelState.IsValid)
            {
                //db.AppCatalog_Database.Add(appcatalog_database);
                //db.SaveChanges();
                return RedirectToAction("Index");
            }

            ViewBag.databaseServerTypeID = new SelectList(db.AppCatalog_ServerType, "servertypeID", "servertypeName", appcatalog_database.databaseServerTypeID);
            return View(appcatalog_database);
        }

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Here is a partial listing of my View:

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true, "", new { @class = "validation-summary-errors" }) 

    <fieldset>
        <div class="editor-field">
            @Html.Label("Server Type", new { @class = "editor-label" }) :
            @Html.DropDownList("databaseServerTypeID", "-- Choose Server Type --")
            <span class="error-msg">@Html.ValidationMessageFor(model => model.databaseServerTypeID)</span>
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.databaseName)
            <span class="error-msg">@Html.ValidationMessageFor(model => model.databaseName)</span>
        </div>

        <div class="editor-field">
            @Html.EditorFor(model => model.databaseDescription)
            <span class="error-msg">@Html.ValidationMessageFor(model => model.databaseDescription)</span>
        </div>

        <p>
            <input type="submit" value="Create" />
        </p>
    </fieldset>
}

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The problem is when I click Create without entering any data, I get the Required Error Messages on the Database Name field and Description Field but not the Server Type Field which is showing -- Choose Server Type -- .

When I enter a database name and description and hit Create, the Required message for the Server Type is displayed.

How do I get the Server Type Required message to display if -- Choose Server Type -- is displayed when Create is clicked?

Any help is greatly appreciated!