调用重写方法

Question

我有以下代码：

public class CustomContentBlock : ContentBlock
{
    public override void Fill()
    {
        this._Item.Html = replace_dangerous_entities(this._Item.Html);
        base.Fill();
    }
}

public class ContentBlock : EkXsltWebPart, IEnumerator, IEnumerable, IListSource, IDataSource, ICallbackEventHandler
{
    protected ContentBase _Item;

    public override void Fill()
    {
        if (this.Dirty && base.CallBackCheck())
        {
            this._FillCount++;
            if (!base.DesignTime)
            {
                if (this.ContentID == 0L)
                {
                    return;
                }
                this.SetContentLanguage();
                this.ReadCachedItem();
                if (this._Item == null)
                {
                    ApiSupport.ContentResult contentResult = base.Connection.api.LoadContent(this.ContentID, base.Connection.api.CmsPreview, this.GetAnalyticsData);
                    if (contentResult.Item != null && Convert.ToInt64(contentResult.Item.ContentType) == 102L)
                    {
                        string pattern = "scrolling=\"yes\"";
                        contentResult.Item.Html = Regex.Replace(contentResult.Item.Html, pattern, "");
                    }
                    if (contentResult.Item != null && contentResult.Item.ContentType == EkEnumeration.CMSContentType.Multimedia && base.Connection.api.CmsPreview && contentResult.Item.Status.ToString().ToUpper() != "A")
                    {
                        string oldValue = string.Concat(new string[]
                        {
                            base.Connection.api.RequestInformationRef.AssetPath, 
                            base.Connection.api.EkContentRef.GetFolderParentFolderIdRecursive(contentResult.Item.FolderId).Replace(",", "/"), 
                            "/", 
                            contentResult.Item.AssetInfo.Id, 
                            ".", 
                            contentResult.Item.AssetInfo.FileExtension
                        });
                        contentResult.Item.Html = contentResult.Item.Html.Replace(oldValue, string.Concat(new string[]
                        {
                            base.Connection.api.SitePath, 
                            "assetmanagement/DownloadAsset.aspx?history=true&ID=", 
                            contentResult.Item.AssetInfo.Id, 
                            "&version=", 
                            contentResult.Item.AssetInfo.Version
                        }));
                    }
                    this.ResetContentLanguage();
                    if (contentResult.ErrorMessage != string.Empty)
                    {
                        throw new Exception(contentResult.ErrorMessage);
                    }
                    this._Item = contentResult.Item;
                    base.NormalizeBase(ref this._Item);
                    if (this._Item != null && !contentResult.Item.IsPrivate && Cache.Cacheable(false))
                    {
                        Cache.PutCache(this._identifier, this._Item, this.CacheInterval);
                    }
                }
                this.CreateDataSet();
                base.CatalogIconImageUrl = base.Connection.api.ApplicationPath + "images/application/icon_document.gif";
                base.TitleIconImageUrl = "";
                base.Title = this._Item.Title;
            }
            this.BuildOutput();
            base.SetClean();
        }
    }
}  

但我总是收到错误消息stackoverflowexception occurred in mscorlib.dll base.Fill();

班级ContentBlock不是我们写的。