SSIS package hits "login failed for user" when simultaneous operations occur against the same target database
Here it is:  the failing login in question was a SQL Server login. Here is how we configured the SQL connection manager properties for old, new, and developer environments:


ServerName - MyServer
InitialCatalog - MyDB
UserName - MyUser
Password - ***********
ConnectionString - Data Source=MyServer;User Id=MyUser;Initial Catalog=MyDB;Provider=SQLNCLI11;Persist Security Info=True;Auto Translate=False;


While this worked perfectly on the old SQL 2008 environment, and it was no problem from Visual Studio, it failed during simultaneous database operations from the SQL 2012 Integration Services Catalog, but started working when we added Password=****** to the connection string.


ConnectionString - Data Source=MyServer;User Id=MyUser;Password=********;Initial Catalog=MyDB;Provider=SQLNCLI11;Persist Security Info=True;Auto Translate=False;


It would seem that if a second simultaneous connection is being opened while in the SQL 2012 Integration Services Catalog execution environment, only the connection string itself (of the initial connection?) is consulted, not Password or other constituent properties of the connection manager.  Therefore, Password has to be in the connection string.