Potential Issue With Backing up Sharepoint, Onedrive, Teams Files, and List Attachments

Backup of SharePoint, OneDrive, and Teams data completes successfully, and subsequent restores of this protected data are successful. However, when opening some of the restored files or list attachments, users may find that these items do not open correctly in their associated applications (e.g., Microsoft Word, Excel, PowerPoint, and Adobe Acrobat).

Common errors reported by customers are:

• “The file is either not a supported file type or has been damaged.”

• “Word found unreadable content…”

• “Excel cannot open the file ... because the file format or file extension is not valid.”

• “Sorry, this document can't be opened for editing.”

The affected files retain their original names and extensions (e.g., .docx, .pdf) but cannot be viewed or edited.

During backup operations, files, list attachments, or images from SharePoint, OneDrive, or Teams were saved with the contents of the HTML error pages returned by the API, rather than their actual file content.

Veeam first observed this issue in early March 2026.

This issue impacts Veeam Data Cloud for Microsoft 365 and all supported versions of Veeam Backup for Microsoft 365. It is independent of repository type, affecting both JET-based and object storage repositories.

No errors are shown in backup jobs or restore tasks; the issue surfaces only when the user attempts to open the restored file.

Veeam Data Cloud for Microsoft 365

No action is required from Veeam Data Cloud for Microsoft 365 users. The platform has been automatically updated to the latest version to address the root cause, ensuring that newly created and changed items are backed up correctly.

Affected items in the backups, if any, that have not changed in production since the last backup remain impacted by the issue. Veeam Data Cloud for Microsoft 365 will remediate the impacted items automatically where possible.
 

Veeam Backup for Microsoft 365

The root cause of the issue described in this article was resolved starting in Veeam Backup for Microsoft 365 v8.4 (build 8.4.0.1457), ensuring that new and changed items are backed up correctly. All Veeam Backup for Microsoft 365 customers are advised to upgrade to the latest version as soon as possible.

Affected items in the backups, if any, that have not changed in production since the last backup remain impacted by the issue. Veeam is working on a solution that will allow customers to remediate the impacted items. This article will be updated when further information is available.