Application-aware backup fails with one of these errors:

Error 1

Error code: 34865165
Fields: {"$module":"aavb_backup_command_addon_vsa64_23140"}
Message: Failed to get the metadata from the 'VMware Snapshot Provider' extension library.
Error code: 65520
Fields: {"$module":"aavb_backup_command_addon_vsa64_23140","code":2147942402}
Message: The system cannot find the file specified

Backup fails with:

The backup has failed because 'VSS Writer' has timed out during snapshot creation



Windows error: (0x800423F2) VSS writer 'System Writer' with class ID 'E8132975-6F93-4464-A53E-1050253AE220' has timed out. This may be caused by too intensive I/O on the machine at the backup start time. Try to re-schedule the backup to some different time. To troubleshoot VSS issues, download and run Acronis VSS Doctor available at


Backup of a Windows machine fails with error:
Logon failure: unknown user name or bad password.


Acronis Cyber Backup agent receives this error from Windows while trying to access backup source or target.

This article describes how to use Web Restore to retrieve files or folders without using Acronis software.

You restore a machine to dissimilar hardware and apply Acronis Universal Restore.

The process completes successfully, but the restored machine goes to BSoD with error "Stop 0x0000007B".


Operation (backup, recovery, cleanup) fails with the following error:

Windows error: (0x8007051F) There are currently no logon servers available to service the logon request


Backup to NAS or a different activity(replication, validation) fails with:

 Windows error: (0x80070544) The validation information class requested was invalid

The recovery of an Exchange database to original location fails with:

Error code: 254
Module: 91
LineInfo: 0x7A0C574AD2E3F5C3
Fields: {"$module":"arx_agent_fork_vsa64_12960"}
Message: It is not allowed to overwrite database <database> during recovery.


You upgraded from Acronis Backup Advanced 11.7 to Acronis Cyber Backup Advanced 12.5 and then to Acronis Cyber Protect 15.

When you try to create or edit a protection plan, the operation fails with the following error:

POR: cannot assign units of different types


Issue in the product.


The issue has been fixed in Build 25729. Please download and install the latest build.


  1. You save backups to an unmanaged location using Version 12 archive format 
  2. Two or more backup archives have the same "Date modified" value

  1. You have a Windows VM with dynamic disks.
  2. You create an agentless backup of this VM using Virtual Appliance.
  3. When you check the backup archive contents, you notice that drive letters are displayed incorrectly.


  1. You are backing up a SharePoint Server.
  2. Backup fails with:

Error code: 54
Module: 482
LineInfo: 5c71ebf434f0c47a
Fields: $module : disk_bundle_vs_38774
Message: Failed to collect all of the data required for single-pass backup of Microsoft SQL Server.
Error code: 4354
Module: 87
LineInfo: e4fe5c9fd5e63de8
Fields: $module : aaib_mssql_backuper_vs_38774


  1. You set up a backup task with cleanup scheme By number of backups and choose to start cleanup before backup.

  2. After you run the backup several times, recovery points in Show backups show one more recovery point than the number of backups specified.


This is by design.

In general, performance is constantly being optimized, so updating to the latest build is always recommended for the best performance of backup and other operations. 

First of all, please check out the general system requirements, described in your product documentation, to make sure that the hardware usage in your particular scenario is actually outside the normal operating parameters of our product. 

To investigate the issue with Acronis support, please collect the following diagnostic information:


You created Acronis Rescue media on a Mac.

When you attempt to back up the machine with macOS using rescue media, the Backup option is not available. Only recovery can be performed.


The current product design does not support backing up macOS using bootable media. 

This applies to all types of bootable media: ISO downloaded from the website, bootable media created under macOS, bootable media created under Windows or Linux.


  1. When you try to manage licenses in Settings > Licenses, nothing happens. The interface just blinks, and the license is not assigned or revoked. No error message is shown. 
  2. Protection plans are executed as if the licenses were assigned correctly.
  3. In the account_server.log (located in \ProgramData\Acronis\AccountServer\Logs), you see error messages similar to the following one:

You set up a backup plan of Windows machine(s) with Policy Rules: [Disk 0] in Items for backup.

Backup fails with errors similar to:

Cannot resolve inclusion rule '[Disk 0]'.

Disk 0 has not been found while processing the 'Disk by number' template

  1. You create a backup using Version 12 format.
  2. An operation with archive (e.g. applying retention rules) fails with the error message

    Failed to lock the file


  • You have upgraded your system from Acronis Cyber Backup 12.5 to Acronis Cyber Protect 15. 
  • After the upgrade, you created new protection plans. When you try to edit a newly created protection plan, there is a spinning loading circle with Reconnecting... message.

This article applies to:

  • All Acronis software


  1. You are installing Acronis software in Windows
  2. Installation fails with:
    The Windows Installer Service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance.


Issue in the Windows Installer.


You are backing up data to QNAP NAS.

When the activity is almost complete, it fails with:

The credentials for location are not specified


Outdated NAS firmware.


Update NAS firmware to the latest version.

If the issue reproduces with the latest version of firmware, collect system information from the affected agent machine, details about NAS(model, firmware version) and contact Acronis Support.


You have installed Acronis Backup Cloud agent for SQL and created a backup plan for a SQL instance.

Backup task fails with this error: "There are no SQL writers." or "The backup of this SQL Server has failed because of a VSS snapshot failure: No SQL writers are found in the operating system."


File-level backup fails with:

Fatal protocol error


Disk/partition backup fails with: 

Windows error: (0x80070001) Incorrect function


Backup, replication or another activity fails with:

The path <path> does not exist.

For example: The path "F:/" does not exist.

Or, in older builds:

Windows error: (0x80070002) The system cannot find the file specified


  1. You enabled two-factor authentication in Cloud console 
  2. Acronis Cyber Backup/Protect software is installed as on-premises deployment
  3. You configure backup to Cloud Storage. Backup fails with the following error:
    The credentials for location <account> are not specified.
    Failed to authorize the user.



Activity fails with:

Windows error: (0x800704C8) The requested operation cannot be performed on a file with a user-mapped section open