>>>>Hi,
>>>>got a strange one at a client's site today.
>>>>
>>>>SQL Server 2016 installed on a Windows Server 2016.
>>>>My VFP app was successfully connecting using SQL Server Native Client 10.
>>>>The client turned off TLS 1.0 and 1.0 on the server and then my VFP app stopped connecting.
>>>>
>>>>We uninstalled Native Client 10.
>>>>
>>>>I changed the connection string to use SQL Native Client 11.0 and {ODBC Driver 17 for SQL Server} and got this error:
>>>>
>>>>"Connectivity error: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified"
>>>>
>>>>I am able to connect using the ODBC applet on the server with both of these drivers.
>>>>
>>>>I am able to connect from a workstation using both those drivers.
>>>>
>>>>I have no idea what could be causing this so would appreciate any suggestions
>>>
>>>Check if you have these ODBC drivers installed ODBC 32 bit.
>>
>>Yes, they appear to be installed because I can create a DSN in the ODBC 32 bit applet and the test connection works.
>
>It works from the ODBC 32 bit applet -- but the connection string in VFP does not???
>Can you show us what your connection string looks like? (hide passwords of course if there are any)

It turns out that the application was successfully connecting but then it creates a temporary VFP database with a connection for some remote views. This database was pointing to a non-existent database using SQL Native Client 10.0 (which was uninstalled) so the error message was accurate. Once I deleted the temp database the system was able to connect properly.
Thanks for all the thoughts and effort (in particular Boris!)