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SharePoint list attachment is not working correctly for one user. Although other users are not getting any error.

Shehroz Ali 20 Reputation points
2026-03-24T16:00:07.1333333+00:00

Error: Encountering issue when uploading attachment Example.pdf: Upload is invalid. Encountering issue when uploading attachment Example.pdf: Upload is invalid. Encountering issue when uploading attachment Example.pdf: Upload is invalid. Encountering issue when uploading attachment Put back to normal 467006 ins Upload is invalid. Encountering issue when uploading attachment Example.pdf: Upload is invalid. Encountering issue when uploading attachment Example.pdf: Upload is invalid.

Microsoft 365 and Office | SharePoint | For business | Windows
Answer accepted by question author
  1. Alexis-NG 14,895 Reputation points Microsoft External Staff Moderator
    2026-03-24T17:13:20.62+00:00

    Hi @Shehroz Ali

    Good day, and thank you for detailing your issue so clearly.

    Since this is happening to only one user while others are working fine, you can rule out a global SharePoint outage or a list-level setting (like attachments being disabled). The "Upload is invalid" error in SharePoint is usually triggered by a conflict between the user's local environment and the SharePoint upload script.

    You can follow this checklist to troubleshoot this:

    1. Browser isolation:

    Most "Upload is invalid" errors are caused by corrupted browser cache or a stale authentication token.

    • Ask the user to try the upload in an Incognito/Private window. If it works there, they need to clear their browser cache and cookies for the SharePoint domain.
    • Ad-blockers or "privacy" extensions can sometimes block the specific POST request SharePoint uses to attach files. Disable extensions one by one if Incognito works but standard mode does not.
    1. File property issues:

    Even if the file name looks fine in the error message, SharePoint can be picky about metadata and file state.

    • Ensure the file name doesn't contain restricted characters: ~ # % & * { } \ : < > ? / | ". Even if the error shows Example.pdf, check if the actual file has trailing spaces or hidden characters.
    • Ensure the file isn't currently open in another program (like Acrobat or Word). If the file is being synced by OneDrive, wait for the blue sync icon to turn into a green checkmark before uploading.
    • Ask the user to rename the file to something generic (e.g., Test1.pdf) and move it to their Desktop before uploading to rule out long file path issues.
    1. SharePoint permissions
    • Go to Site Settings > Site Permissions. Remove the user from the group entirely and then re-add them. This forces a refresh of their User Information List entry.
    • If your site uses fine-grained permissions, ensure the "Limited Access User Provider" feature isn't interfering. Usually, though, a simple re-addition fixes the "invalid" token issue.
    1. Power Apps issue:

    If your SharePoint list uses a customized Power Apps form instead of the standard SharePoint panel, the "Upload is invalid" error is very common if:

    • The "MaxAttachments" property in the Power Apps attachment control is set to a number the user has already reached.
    • There is a required field on the form that hasn't been filled out yet, which prevents the attachment from "committing" to the record.
    1. Contact Microsoft Support:

    If the issue persists after you verify the possible causes, you can reach out to Microsoft Support through the Microsoft 365 Admin Center so Microsoft can collect logs and investigate your issue. 

    Microsoft also provides customer service phone numbers based on your region. You can find the appropriate contact number here: Customer service phone numbers - Microsoft Support 

    This route ensures that a Microsoft support engineer can initiate a remote session to investigate backend configurations, run advanced diagnostic tools, and, if necessary, escalate the case to specialized teams with access to internal systems and logs. These backend resources are essential for resolving issues that go beyond what’s visible in the user interface.

    As community moderators, we’re here to guide you, but due to privacy and security limitations, we don’t have access to the backend tools required for a full resolution. For this reason, contacting Microsoft Support via the Admin Center is the most secure and efficient way forward.

     

    I hope this helps you resolve the issue quickly. I’m glad to assist and truly hope the information provided has been useful. Please feel free to reach out anytime if you need further assistance.  

    If you find my post helpful, kindly consider marking it as the accepted answer. Doing so can assist others in the community who may have similar questions in finding solutions more quickly.  

    Thank you for your kindness and contributions to the forum.

    Note: Follow the steps in our documentation to enable email notifications if you want to receive email notifications related to this topic.

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  1. Q&A Assist
    2026-03-24T16:00:29.95+00:00
    AI generated content. This question contains an answer created with AI from Q&A Assist. Learn more

    The error for a single user uploading a SharePoint list attachment is consistent with known SharePoint Online attachment issues.

    Based on documented behavior, validate the following for the affected user and item:

    1. Check if the same file name already exists on the list item
      • In classic view, if an attachment is deleted and the same file (or same file name) is immediately reattached before saving, SharePoint can return an error similar to "A file with the name already exists."
      • Workaround:
        1. Edit the list item.
        2. Delete the existing attachment.
        3. Click Save.
        4. Edit the item again, attach the file, then Save.
      • Alternatively, upload the file with a different file name (for example, Example_1.pdf).
    2. Validate the file name against SharePoint restrictions
      • Ensure the file name does not contain invalid characters:
        • Invalid characters: \ / : * ? " < > | # { } % ~ &
      • Ensure there are no patterns that SharePoint rejects, such as multiple periods before the extension (for example, Example..pdf or Name, Ph.D..pdf).
      • If the file name is invalid:
        1. Save the file locally with a valid name (no invalid characters, single period before extension).
        2. Reattach the renamed file to the list item.
    3. Compare behavior with another account on the same machine
      • Have another user log into the same device and try uploading the same Example.pdf to the same list item.
      • If it works for others but not for the affected user on the same device, check for:
        • Browser cache/cookies issues (clear cache/cookies and retry).
        • Try another browser or InPrivate/Incognito session.
    4. Test with a different file
      • Ask the affected user to upload a different small test file with a simple name (for example, Test1.pdf).
      • If the test file works but Example.pdf fails, the issue is likely the specific file name or content; rename Example.pdf and retry.

    If the issue only occurs when reusing the same file name after deletion on that item, use the save-then-reattach pattern or change the file name as a permanent workaround.

    References:

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