In .NET 1.1 , If you write code like this Cache.Add("key",DateTime.Now.ToString(),new System.Web.Caching.CacheDependency(@" C:/Common.config "),System.Web.Caching.Cache.NoAbsoluteExpiration,System.Web.Caching.Cache.NoSlidingExpiration,System.Web.Caching.CacheItemPriority.Default,null); please pay attention to the filename, even this file path is valid and you will always get the error that say invalid file name for monitoring. So what happend? Permission? Or Any IIS Lock Software? hehe, the problem