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 is working expeditiously to resolve this issue with an upcoming release; until that time, all customers are advised to review the following with their technical and governance teams:

• Avoid deleting and overwriting critical files, and list attachments in the production environment.

• Temporarily adjust the Microsoft 365 retention and lifecycle policies (e.g., retention labels/policies, auto-expiration, scheduled cleanup) to prevent the removal or permanent deletion of such content, so that it remains in production.

Veeam Data Cloud for Microsoft 365

No action is required from Veeam Data Cloud for Microsoft 365 users. The platform will be automatically updated to the latest version, fixing the issue.
 

Veeam Backup for Microsoft 365

Veeam is working on a new product version that fixes the root cause of this issue. We will notify you when it becomes available.