Hi MABS-MAN
Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.
Ensure the Azure Backup Agent is updated to at least version 2.0.9249.0. If you upgraded to version 2.0.9273, check that it is properly installed and registered with your backup server.
Check that there is stable network connectivity between the MABS server and Azure, including verifying that no firewalls or proxy settings are blocking access to Azure services.
Ensure that the Microsoft Azure Recovery Services (MARS) agent and the OBEngine service are running. You can check this in the Services console on your server. If OBEngine is not running, start it using the command.
net start OBEngine
Make sure there is enough free space (5-10%) on the scratch folder used by MABS for backups.
Check that an encryption passphrase is configured for your backup server. If it's not set, you'll need to configure one, as it can impact backup operations.
Since the online registration status is fine, make sure both the original and external servers are registered to the same Recovery Services vault to avoid authorization issues.
If the issues continue, try re-registering the MABS server with your Recovery Services vault using the updated credentials downloaded from the Azure portal.
For reference, please review this documentation:-
https://support.microsoft.com/en-us/topic/update-rollup-1-refresh-for-microsoft-azure-backup-server-v4-45688e25-44db-4703-9ae9-cac611e46e07
https://support.microsoft.com/en-us/topic/update-rollup-1-for-microsoft-azure-backup-server-v4-c74acba2-7dce-469e-bc14-f8f885b206ab
https://learn.microsoft.com/en-us/azure/backup/backup-azure-mars-troubleshoot
If you have any further queries, do let us know.
If the answer is helpful, please click "Upvote it".