SQL Server Instance fails to expand in the selection list or backup jobs are failing.

Problem

Trying to expand the SQL Server Instance in the backup selection list fails with one of the below error messages.
Any previously created backup jobs started to fail with either of the following error messages:
"Unable to attach to a resource."
"Microsoft SQL Server does not appear to be running or network connections are preventing access to it."

Or

SQL backup selections expand and the Backup job fails with "An attempt to connect to SQL Server has failed. The logon account may have invalid credentials, or the logon account may have been applied to the wrong resource.".

Error Message

An attempt to connect to SQL Server has failed. The logon account may have invalid credentials, or the logon account may have been applied to the wrong resource.
 

0xe000848c - Unable to attach to a resource.
UMI Code: V-79-57344-33932

0xe0009415 -Microsoft SQL Server does not appear to be running or network connections are preventing access to it.
UMI Code: V-79-57344-37909

V-79-57344-893 - Snapshot Technology: Initialization failure on: "<sqlserver>\<instance>". Snapshot technology used: Microsoft Volume Shadow Copy Service (VSS). Snapshot technology error (0xE000037D): An attempt to connect to SQL Server has failed. The logon account may have invalid credentials, or the logon account may have been applied to the wrong resource.

Cause

These issues can be caused by:

• The Backup Exec account does not have the correct credentials in the SQL Instance.

OR

• SQL Server (INSTANCE NAME) service is not running or is in a disabled state on the SQL server.

OR

• There is a NETBIOS Resolution issue within the environment.
  
   

Solution

• dbcreator
• securityadmin
• serveradmin
• sysadmin

Confirming and/or configuring the Backup Exec Service Account(BESA) to the 'db_owner' role using Microsoft SQL Server Management Studio or Studio Express.

Note: An alternate logon account can added to Backup Exec logon accounts and specified to backup a  SQL server with different credentials than the defined “System Logon Account” aka "Backup Exec Service Account".  The SQL server can be in the same domain, different domain, or a workgroup.  The Logon account must have local admin rights to the server AND rights to the SQL instance. On the Backup/Restore tab change the credentials for the SQL server to the alternate logon account. 

2.  Add the Backup Exec account to local administrator group on SQL server.

3. Ensure that SQL server is online and SQL instance is accessible from Backup Exec server using UDL test: How to perform a quick test connection to the SQL instance.

4. Ensure the SQL Server(INSTANCE NAME) service is running and not in disabled state on the SQL server.

5. Add the SQL Server in Backup Exec via the IP address and if the SQL databases are now selectable and the backups are successful, verify your NETBIOS settings within the environment.