- Your database has SINGLE_USER access and it has been already opened. Make sure no one uses the database during backup or change the access mode.
- Name of the database has leading/trailing spaces or unprintable characters. Fix the database name by removing the unsupported characters.
- Microsoft Volume Shadow Copy Service (VSS) and SQL Server VSS Writer Service are not running or unstable. Check system logs and solve the issue.
- Lack of worker threads. Try to increase the Max Worker Threads configuration option of MS SQL Server.
Depending on the configuration of a SQL Server, available threads can be used if you create a snapshot backup of many databases at the same time. Microsoft has an article referring to the issue and its workaround:
- If you are running a 64-bit version of SQL Server, you can consider increasing the Max Worker Threads configuration option
- If you are running a 32-bit version of SQL Server, check the influence of increasing of Max Worker Threads on server performance
***** In order to complete the backup successfully you will need to configure 5 Worker Threads for each SQL instance, for example: if you have 10 SQL instances (databases) you will need to configure 50 Worker Threads in the Max Worker Threads option. *****