DataAccess打开数据库连接Error
System.Data.SqlClient.SqlException: 已成功与服务器建立连接，但是在登录过程中发生错误。 (provider: TCP 提供程序, error: 0 - 指定的网络名不再可用。)
   在 System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   在 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   在 System.Data.SqlClient.TdsParserStateObject.ReadSniError(TdsParserStateObject stateObj, UInt32 error)
   在 System.Data.SqlClient.TdsParserStateObject.ReadSni(DbAsyncResult asyncResult, TdsParserStateObject stateObj)
   在 System.Data.SqlClient.TdsParserStateObject.ReadNetworkPacket()
   在 System.Data.SqlClient.TdsParserStateObject.ReadBuffer()
   在 System.Data.SqlClient.TdsParserStateObject.ReadByte()
   在 System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   在 System.Data.SqlClient.SqlInternalConnectionTds.CompleteLogin(Boolean enlistOK)
   在 System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, Int64 timerExpire, SqlConnection owningObject)
   在 System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String host, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, Int64 timerStart)
   在 System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance)
   在 System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance)
   在 System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection)
   在 System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options)
   在 System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject)
   在 System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject)
   在 System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
   在 System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
   在 System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
   在 Syste