SQL Server Plugin Backup Fails with a 'Failed to login to SQL Instance' error message. (4037723)

NetVault Backup environment details:

NetVault Server:
- Windows Server 2012 (Not R2).
- Version 10.0.1
- Windows Firewall: Disabled.

NetVault Client:
- SQL 2008 Express Server standalone version.
- Windows Server 2008 R2
- Version 10.0.1.24
- SQL Server Plug-in version 10.0.1.15
- Windows Firewall: Disabled.

Binary log shows the following messages and errors:

1] Job Message   2014/11/30 22:36:16   194   Data Plugin   PIAB   ODBC message: [Microsoft][ODBC SQL Server Driver][DBMSLPCN]SQL Server does not exist or access denied.
2] Job Message   2014/11/30 22:36:16   194   Data Plugin   PIAB   ODBC message: [Microsoft][ODBC SQL Server Driver][DBMSLPCN]ConnectionOpen (Connect()).
3] Error   2014/11/30 22:36:16   194   Data Plugin   PIAB   Failed to login to SQL Instance 'PIAB\SQLEXPRESS'
4] Error   2014/11/30 22:36:16   194   Data Plugin   PIAB   Unable to backup data due to empty backup list
5] Job Message   2014/11/30 22:36:16   194   Jobs   NETVAULT   Finished job 194, phase 1 (instance 17)

The following error message was displayed when browsing the SQL Plugin within the Backup window:

“Backup not allowed. Check Configuration and Plug-in Edition License”.

There was already an SQL Server Plugin license key installed on the Client (…\NetVault Backup\db\bkl directory) and the backup was working before.

When trying to see what the configuration of the SQL Plugin had, all the fields were empty.
There was a possibility that the configuration had corrupted i.e. gone missing, or that the license had corrupted and therefore stopping you seeing the configuration details.

Made sure that SQL Plugin had been configured correctly as per all of Chapter 3 of the SQL Server Plugin Users Guide on the following link:

https://support.quest.com/netvault-backup/technical-documents

Re-installing the SQL Server Plugin license key on the Client again didn't resolve the issue either.

Cause 1 - Refer to Workaround 1

SQL Server service is not started

Cause 2 - Refer to workaround 2

NetVault was not able to figure out the default instance.

WORKAROUND 1

The problem was that the SQL Express services hadn't started on the respective servers.

WORKAROUND 2

If this is a single instance SQL server, from the Configure screen provide/input "(local)" [without the quotes] in the "target instance" field.