The issue may be related to a VSS issue. For further troubleshooting of VSS issues, see Acronis Cyber Backup: VSS Troubleshooting Guide
The issue may also be with that there is not enough space in the temporary folder to create the snapshot. See Acronis Cyber Backup Creates a Temporary File During Snapshot.
The issue may also be with that some non-Acronis process consumes system resources (not necessarily system memory). As a result, the task fails. See Acronis Product Fails to Back Up with "Insufficient system resources exist to complete the requested service (0xFFF0)".
The issue may also be due to disk errors:
- Please download Acronis Report and run it on the machine;
- Running Acronis Report will produce text file that contains important information about your disks. The name of the file is report.txt;
- Open report and take a look at the right-hand column:

If it has an "E" letter as in the example above, this means that the disk has errors and needs to be checked. Identify the disk with errors as show on the screenshot in green The disk letter is displayed in the "O" column.
- Check the disk for errors:
- Go to the Command Prompt (Start-Run -> cmd):

- Enter the command:
chkdsk DISK: /r
where DISK is the drive letter of the partition you need to check. Please note that checking the C: drive may require you to reboot the machine.
For example

- Reattempt the backup operation and see if the issue is resolved.
If the issue persists, please create a system report as described in AcronisInfo Utility. Please send your support request to Acronis Support and attach the system report and Acronis Report files to your request.