Hi Everyone, I setup database mirroring between two NAMED instances on two different servers. After completeing the database mirroring configuration, I clicked on Start Mirroring button then I got below error message. Both Named instances are running on other than default ports (1434) and mirror endpoints ports are 5022. An Error occurred while starting mirroring Alter failed for Database Test (Microsoft.SqlServer.Smo) An exception occured while executing a Transact-SQL statement or batch. Alter Database Command failed due to an invalid server connection string. (Microsoft SQL server, Error: 1449). For testing purpose, I installed two named instances on one test box and configured database mirroring and that is working fine. so it seems the problem with two instances on DIFFERENT Servers. Any help is greatly appreciated.