Job may report warning: "Failed to finalize guest processing. Details: Failed to process 'TruncateSQLLog' command. Failed to truncate transaction logs for SQL instances: <instance name>. Possible reasons: lack of permissions, or transaction log corruption."
SQL logs truncation is done under user account specified in AAIP in Job settings, if it fails then GuestHelper tries to truncate transaction logs under LocalSystem account.
In order to understand why SQL logs truncation failed you will need to open the GuestHelper log in Guest VM:
\\GUESTVM\c$\ProgramData\Veeam\Backup\VeeamGuestHelper_%date%.log (for Windows 2008 or higher)
\\GUESTVM\c$\Documents and Settings\All Users\Application Data\Veeam\Backup\VeeamGuestHelper_%date%.log (for Windows 2003)
Then do search within the log using keyphrase "Truncation Statistics"
1) Error: OpenFromInitializationString failed. [Login failed for 'DOMAIN\user'.]
Solution: give DOMAIN\user permissions on SQL instance and add db_backupoperator role for all FULL and BULK databases, or give it a sysadmin role.
2) OLEDB Error: 'The server principal "DOMAIN\user" is not able to access the database "DATABASE" under the current security context.', HelpCtx: '0'
Solution: give DOMAIN\user db_backupoperator role for all FULL and BULK databases, or give it a sysadmin role.
3) OLEDB Error: 'BACKUP detected corruption in the database log. Check the error log for more information.', HelpCtx: '0'
Solution: error points to possible corruption and issues with SQL server
4) OLEDB Error: 'BACKUP LOG cannot be performed because there is no current database backup.'
The issue occurs when the secondary node has always been backed up with "copy only" flag and its standalone DBs do not have any full backup. Thus during the truncation of the standalone DB logs we get the above-mentioned message.
The same solution applies if you get this message with regard to the excluded vCenter database / Veeam database.
Solution: Implement the following registry value in affected VMs in [HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup and Replication\] and [ HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\VeeaM\Veeam Backup and Replication] (if there is no latter, you will need to create it):
Default value: 60 (in seconds, decimal)
Try to expand that value and run a backup afterwards, safe guess here is to set it for 600 seconds.
If you observe the following warning "Failed to truncate transaction logs for SQL instances: MICROSOFT WID" on Veeam B&R version 220.127.116.114, please contact Veeam Support for the hot-fix.