Unable to migrate MSSQL database using Plesk migrator: Connection to the database failed for an unknown reason

Symptoms

Migration & Transfer Manager shows the following error:

[Migration] Failed to copy content of database 'dbname_'
Migration tools tried to perform operation in 3 attempts: Failed to execute SQL query: Connection to the database failed for an unknown reason. 
Query: BACKUP DATABASE [dbname_] TO DISK=%(file)s 
Arguments: {'file': u'C:migratormssql-dumpsdb_backup_example.com_dbname_.sql'} 
Server: 127.0.0.1SQLExpress 
User: sa 
Tried to connect from: 203.0.113.2

Cause

SQL server browser service is not running on the source server.

Resolution

1. Connect to the server via RDP.

2. Open services management snap-in: Start menu > Run > services.msc.

3. Double-click SQL Server Browser, set Startup type to Automatic, and start the service manually:

   

4. Restart the migration on the target server.