This issue occurs when the password of the "Administrator user" specified in Instance Configure dialog box of the Plug-in for SQL Server settings has been changed.
The process of displaying a tree on the Selection set screen and the one of executing backup are different as detailed below. Since nvcoreplg is started by the local "SYSTEM" user, it is not affected by the password change of the administrator user.
- Process of displaying Plug-in for SQL Server tree on the backup screen.
nvcoreplg | Process execution user: SYSTEM (default).


- Backup and restore execution process.
nvsqlserver | Process execution user: User specified in Plug-in for SQL Server settings