电商升级V6库访问 小组 出现这个错误，请问怎样解决？
异常信息：引发类型为“System.Web.HttpUnhandledException”的异常。
Source:System.Web
StackTrace:   在 System.Web.UI.Page.HandleError(Exception e)
   在 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   在 System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   在 System.Web.UI.Page.ProcessRequest()
   在 System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
   在 System.Web.UI.Page.ProcessRequest(HttpContext context)
   在 ASP.index_aspx.ProcessRequest(HttpContext context) 位置 c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\54c4d416\3593751b\App_Web_prieuxun.0.cs:行号 0
   在 System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   在 System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   在 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

InnerException:System.Reflection.TargetInvocationException: 调用的目标发生了异常。 ---> System.MissingMethodException: 找不到方法:“System.String Kesion.HtmlTags.Function.ReadFile(System.String)”。
   在 Kesion.Controllers.groupController.LoadBBSIndex(Boolean isMobileDevice)
   在 Kesion.Controllers.groupController.Run(Boolean isMobileDevice)
   --- 内部异常堆栈跟踪的结尾 ---
   在 System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   在 System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   在 System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   在 Kesion.NET.WebSite.Index.Page_Load(Object sender, EventArgs e)
   在 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   在 System.Web.UI.Control.OnLoad(EventArgs e)
   在 System.Web.UI.Control.LoadRecursive()
   在 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)