SharePoint or OneDrive Backup fails with 'Cannot complete this action'

Issue Recurrence - July 20, 2026
Veeam Technical Support is tracking several recent cases where the issue reported in this article is occurring. This recurrence is under investigation, and this notice will be updated as further information becomes available.

Update - July 27, 2026
To remediate this situation for Veeam Backup for Microsoft 365 deployments, update the OneDriveChildPageSize value for each backup proxy or proxy pool that is running an affected backup.
The following variables should be used with the example scripts on the user guide page documenting the usage of Set-VBOConfigurationParameter.

$xpath = "/Veeam/Archiver/Source"
$key = "OneDriveChildPageSize"
$value = "150"

Note: Ensure that the Veeam.Archiver.Proxy service on the proxy(s) is restarted after the setting is changed by adding the -Restart switch to the Set-VBOConfigurationParameter command.

For Veeam Data Cloud for Microsoft 365, the fix has already been deployed on the backend, and no customer action is required.