You are using Acronis Backup Cloud or the cloud deployment of Acronis Backup 12.5.
Backup fails with: The password for the protected backup is incorrect.
You check pcs log (in C:\ProgramData\Acronis\BackupAndRecovery\MMS\) and see these errors:
2018-08-21T20:05:37:454-04:00 2804 W00000000: cl#21: TLS connect failed with error 'error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate'
2018-08-21T20:05:37:454-04:00 2804 W00000000: cl#21: connected to XXX.XXX.XXX.XXX:44445, but failed to start a session with a gateway: -3 (Authentication failure due to wrong credentials)
A network issue prevented establishing TLS-secured connection between Acronis Agent and Acronis Cloud.
If the problem recurs, the possible causes could be firewall interfering with certificates exchange between Acronis Agent installed on the affected machine and Acronis Management Server in Acronis cloud or an attempt of a man-in-the-middle attack.
Exclude Acronis folders and executables from antivirus and other security programs: see KB36429.