Please see the more recent and detailed article:
Cannot perform the requested operation on an item that does not exist. Type: Xceed.FileSystem.DiskFile
If you run a backup job manually, it successfully work, however, when it runs as a scheduled job it fails with the error message: “Cannot perform the requested operation on an item that does not exist. Type: Xceed.FileSystem.DiskFile”, you can around this issue with one of the below solutions.
The server principal “NT AUTHORITY\SYSTEM” is not able to access the database “database-name” under the current security context
If you encounter the error message: “The server principal “NT AUTHORITY\SYSTEM” is not able to access the database database-name under the current security context”, you will find the solution below:
Go to the “SQL Server” sections and click on gear button. At the opened “Connect to SQL Server on this computer” window you need select “Windows Authentication” and enter User Name and Password. Press “Test SQL Server Connection” to make sure that you have specified the correct data and then click on “Save & Close” to save and apply new settings. More…