MS SQL Server does not allow log truncation for databases that do not have native full backups. Create a native SQL full backup of that database once
- You perform a a single-pass backup with the Truncate MS SQL Server logs option enabled;
- After the operation completes, you see an information message in the logs similar to the following one:
Cannot truncate the transaction logs of SQL database 'name' because there is no full backup of this database
MS SQL Server does not allow log truncation for databases which do not have native full backups. Instead, MS SQL Server automatically truncates logs of such databases by checkpoints. See SQLServerGeeks: Auto-Truncate Log in Full Recovery Model.
Thus, Acronis Backup Advanced for SQL cannot truncate logs as well.
Create a native MS SQL Server full backup of that database at least once. See MSDN: Create a Full Database Backup (SQL Server).