System.Data.sqlClient.sqlException: A network-related or instance-specific error occurred while establishing a connection to sql Server. The server was not found or was not accessible. Verify that the instance name is correct and that sql Server is configured to allow remote connections. (provider: Named Pipes Provider,error: 40 - Could not open a connection to sql Server)

Generated: Wed,02 May 2012 05:05:21 GMT

System.Data.EntityException: The underlying provider Failed on Open. ---> System.Data.sqlClient.sqlException: A network-related or instance-specific error occurred while establishing a connection to sql Server. The server was not found or was not accessible. Verify that the instance name is correct and that sql Server is configured to allow remote connections. (provider: Named Pipes Provider,error: 40 - Could not open a connection to sql Server)
   at System.Data.sqlClient.sqlInternalConnection.OnError(sqlException exception,Boolean breakConnection)
   at System.Data.sqlClient.TdsParser.ThrowExceptionAndWarning()
   at System.Data.sqlClient.TdsParser.Connect(ServerInfo serverInfo,sqlInternalConnectionTds connHandler,Boolean ignoreSniOpenTimeout,Int64 timerExpire,Boolean encrypt,Boolean trustServerCert,Boolean integratedSecurity)
   at System.Data.sqlClient.sqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo,String newPassword,TimeoutTimer timeout,sqlConnection owningObject)
   at System.Data.sqlClient.sqlInternalConnectionTds.LoginWithFailover(Boolean useFailoverHost,ServerInfo primaryServerInfo,String failoverHost,Boolean redirectedUserInstance,sqlConnection owningObject,sqlConnectionString connectionOptions,TimeoutTimer timeout)
   at System.Data.sqlClient.sqlInternalConnectionTds.OpenLoginEnlist(sqlConnection owningObject,Boolean redirectedUserInstance)
   at System.Data.sqlClient.sqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity,Object providerInfo,Boolean redirectedUserInstance)
   at System.Data.sqlClient.sqlConnectionFactory.CreateConnection(DbConnectionOptions options,Object poolGroupProviderInfo,DbConnectionPool pool,DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection,DbConnectionOptions options)
   at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection,DbConnectionFactory connectionFactory)
   at System.Data.sqlClient.sqlConnection.Open()
   at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition,DbConnection storeConnectionToOpen,DbConnection originalConnection,String exceptionCode,String attemptedOperation,Boolean& closeStoreConnectionOnFailure)
   --- End of inner exception stack trace ---
   at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition,Boolean& closeStoreConnectionOnFailure)
   at System.Data.EntityClient.EntityConnection.Open()
   at System.Data.Objects.ObjectContext.EnsureConnection()
   at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator()
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at System.Data.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__2[TResult](IEnumerable`1 sequence)
   at System.Data.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable`1 query,Expression queryRoot)
   at System.Data.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
   at MyApp.Data.UserRepository.GetUserDetails(String username)
   at MyApp.Core.Services.SiteService.GetUserDetails(String username,Int64 userId)
   at MyApp.PublicSite.Web.Controllers.BaseController.Initialize(RequestContext requestContext)
   at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
   at MyApp.PublicSite.Web.Controllers.BaseController.Execute(RequestContext requestContext)
   at System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext)
   at System.Web.Mvc.MvcHandler.<>c__DisplayClass6.<>c__DisplayClassb.<BeginProcessRequest>b__5()
   at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass1.<MakeVoidDelegate>b__0()
   at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
   at System.Web.Mvc.MvcHandler.<>c__DisplayClasse.<EndProcessRequest>b__d()
   at System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f)
   at System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action)
   at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
   at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step,Boolean& completedSynchronously)

连接字符串是：

<connectionStrings>
    <add name="MyAppDBContainer" connectionString="Metadata=res://*/MyAppDB.csdl|res://*/MyAppDB.ssdl|res://*/MyAppDB.msl;provider=System.Data.sqlClient;provider connection string=&quot;data source=SERVERNAME;initial catalog=MyAppDB;persist security info=True;user id=USERID;Password=PASSWORD;multipleactiveresultsets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
  </connectionStrings>

这个异常是随机发生的,不能每次得到/再生.任何可能的设置,我可能会在这里丢失？请建议.