DDBEA 4.5 - with SQL 2014 and 2016 on the same system - Cannot log in to SQL Server instance.

Data Domain Backup Enterprise Agent - DDBEA plugin fails to perform any SQL Server backups.
 

ddbmsqlsv NSR critical Cannot login to SQL Server Default Instance.

ddbmsqlsv: Unable to complete the SQL connection

Environment
SQL Server 2014 is installed, and one SQL 2014 instance is running.  SQL Server Management Studio (SSMS) is using version 2014. 
On the same system, SQL Server 2016 software is also installed.

Checked permissions of the logged-on user and it has all required permissions. 
User can perform Native SQL backups, from SSMS, OSQL, and SQLCMD tools.

Investigation revealed, sometime after SQL Server 2016 was installed that either.

•  SQL 2016 software was partially uninstalled (but not completely)
•  Or some files from SQL 2016 installation were deleted.      This caused SQL 2016 ADO.Net drivers to be removed.  ** These drivers are necessary for DDBEA to connect to SQL Server instance.
• The SQL Server instance and SSMS, which are both version 2014, have no issues.
• The SQL Server 2016 software was not removed correctly or completely, this caused any installation of DDBEA to try connecting using missing SQL 2016 ADO.net drivers.

Any backup of any database fails with the error. 

 ddbmsqlsv NSR critical Cannot login to SQL Server Default Instance.
 ddbmsqlsv: Unable to complete the SQL connection

To resolve,

First uninstall DDBEA.   Then, perform One of the following:

A)  if the required SQL version is 2014, then Un-Install and then Re-Install SQL Server 2014 

B)  if the required SQL version is 2016, and it was not uninstalled correctly, then perform fresh install of SQL Server 2016. 

After the above, reinstall DDBEA.