ODBC connection to SQL Server 2008 R2

On ODBC  using SQL Native Client.
Many possible problems. But consider trying with Server Firewall off. If this is successful then consider the following changes on firewall which have worked for me.

Firewall settings on server are:

http://technet.microsoft.com/en-us/library/ms175043.aspx

On the Start menu, click Run, type firewall.cpl and then click OK.

In the Windows Firewall dialog box, click the Exceptions tab, and then click Add Port.

In the Add a Port dialog box, in the Name text box, type SQL Server <instance name>.

In the Port number text box, type the port number of the instance of the Database Engine, such as 1433 for the default instance.

Verify that TCP is selected, and then click OK.

To open the port to expose the SQL Server Browser service, click Add Port, type SQL Server Browser in the Name text box, type 1434 in the Port Number text box, select UDP, and then click OK.

Note
To allow named pipes access through the firewall, you must also enable File and Printer Sharing through the firewall.

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Also Firewall on server must add program SQLServer.exe which is at <program files><Microsoft SQL Server><MSSQL10_50.Instance Name\MSSQL\Binn\sqlservr.exe

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Prefer not using older ODBC SQL server, but if do then on client configuration dynamically chosen ports is relevant