Index and length must refer to a location within the string. Parameter name: length

at System.String.Substring(Int32 startIndex, Int32 length) at UniversalWEBPlatform.MODLayout.GetImageFromHTMLForHeader(List`1& ElencoIMGFetch, List`1& ElencoIMG, String HTMLString) at UniversalWEBPlatform.MODLayout.CostruisciPagina(Pagina& Pagina, String RouteString, HttpServerUtility& Server, HttpResponse& Response, HttpRequest& Request, HttpSessionState Session, DataClass BaseClass, ParameterRetHtmlString& Parameter, List`1& ElencoIMG, List`1& ElencoIMGFetchPrefer, String& CanonicalLink, String& MasterTitleString, String& MasterDescriptionString, Boolean& HasCheckOUT, String& MasterMetaOGString, Boolean Preview) at UniversalWEBPlatform.Pagina.Page_Load(Object sender, EventArgs e)