Acronis Backup Cloud / Acronis Backup Service: Backup Fails with "Key not valid for use in specified state"

Symptoms

1. You create a backup plan and set up encryption.
2. After a while, you change the user running Acronis Managed Machine Service on the protected machine.
3. Backup fails with:

| Error
| Backup failed

| Key not valid for use in specified state
| Error code: 65520
| Module: 0
| LineInfo: 0x36E942E8021F4B85
| Fields: {"$module":"security_core_vsa64_2406","code":"2148073483"}
| Message: Key not valid for use in specified state