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, fixing the root cause and ensuring future backups will be consistent.
 

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).
All Veeam Backup for Microsoft 365 customers are advised to upgrade as soon as possible to ensure future backups will be consistent.