Sql-server – 32Bit ODBC DSN “Server does not exist or access denied” but 64 bit ODBC OK connecting to SQL Server 2014

There are two ODBC dialogs on your system. One for 32bit and one for 64bit. The one you can reach via system control is the 64bit one.

The 32bit version is located at

• C:\WINDOWS\SYSTEM32\ODBCAD32.EXE (on a 32bit Windows)
• C:\WINDOWS\SYSWOW64\ODBCAD32.EXE (on a 64bit Windows)

It seems that what you want to achieve is not possible using that client.

The issue is a result of older SQL clients (specifically using MDAC sqlsvr32.dll driver) perform an "InstanceValidity" check when connecting to SQL Server. The driver passes "MSSQLServer" as the instance to verify for the InstanceValidity check. In this case, since the instance name listening on the Default port (1433) is named "Instance01" and "Instance02", it fails because the Instance names do not match the InstanceValidity check.

According to what is most convinient for you in this case you might need to specify the port on your client, change your client, or change your named instance to be your default instance.

Source: http://social.msdn.microsoft.com/Forums/sqlserver/en-US/7f353b59-7e7f-4ec3-adcb-e69ca2629b21/named-sql-2008-r2-server-listening-on-default-port-1433-with-dedicated-ip-address-requires-port?forum=sqldataaccess