Are you using SQL Server 2012 Express? Don't miss the server name syntax Servername\SQLEXPRESS where you substitute Servername with the name of the computer where the SQL Server 2012 Express installation resides.
When to use SQL Native Client?
This connection string (Standard security using SQLNCLI11 OLEDB) can be used for connections to
SQL Server 2012.
Start over in the connection string reference index.
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