Acronis Backup 12: backup of virtual machines fails with "The management server is not available for more than 30 days"

Symptoms

1. You are backing up VMware virtual machines with Acronis Virtual Appliance.
2. After a while, backups start failing with this error:
   Error code: 150
   Module: 664
   LineInfo: 0x2D3A16DFCF3A644E
   Fields:{"TimeoutSeconds":"3048294","$module":"agent_protection_addon_glxa64_3602"}
   Message: The management server is not available for more than 30 days.

Cause