1. You installed Acronis Backup 12.5 Update 4 (build 13400 and higher),
2. When you navigate to Settings -> Agents -> Details, you see that Agent is shown offline since year 1754 (exact date depends on your environment). You cannot run a backup plan on this machine or apply new backup plans to it.
Issue in the product.
Acronis Development team is working on fixing this issue in next version of Acronis Backup 12.5.
Use the following workaround:
- On the Management Server, disable IPv6 protocol in network adapter properties: right-click on the Network icon on the system tray and click on Open Network & Internet Settings -> Change Adapter Options -> right-click on your network adapter and select Properties. Uncheck Internet Protocol Version 6 checkbox:
- Restart Acronis Service Manager service;
- Manually add the affected machine to Management Server using RegisterAgentTool: see this article for instructions;
- If needed, reenable IPv6 protocol in network adapter properties, then restart Acronis Service Manager service.
If suggested steps did not resolve the issue, collect Acronis System Information from the Management Server and affected Agent machine and contact Acronis Customer Central with reference to this article.