Connection failed : SQL state S1 T00 SQL SERVER ERROR 0. login timeout expired (1 Viewer)

Hi all,
I am stuck with one issue on my access migrated to sql backend. It was suggested that apart from migrating the access tables to the Sql backend I should create a ODBC connection from the access front end to the SQL server (2010). I recently updated the license of the server and ever since that I have been getting ODBC errors. This one in particular keep reoccurring. CAN U PLEASE HELP ME. I have attached a snapshot of the error .

Are you using the default ODBC on each Client workstation to connect?
What is the OS of the Server hosting SQL Server.
Do all logins fail everytime? Or is it just some workstations? Is it intermittent?

Does your ODBC use Network Security or SQL Server Security?
It is worth setting up a SQL Server Security Admin account
UN: MyTestUser PW: (a password)
ODBC allows for the two different types of login.
See if one is working while the other one does not work.
There are known errors on MSDN for network security when updating server licnese.
At any rate, a MyTestUser login can really help with understanding if it is a network problem, a SQL Security problem or other issues.

My real suggestion would be to install SQL Server Native Client (free download) and write vba code to create a DSN-Less connection. There are plenty of great examples on this site.
Creating Linked Tables with code offers a better degree of control.
The SQL Server Native Client is a ODBC dll that can be downloaded onto each client workstation. It is also used for AZURE. Otherwise, we can get into what is the version for each DLL for each workstation's ODBC drivers.
That said, there is great examples for using VBA for the ODBC drives on this forum as well.