Specific User Cannot Share Files Over Teams

Dear @O'Connell, Theo,

Thank you for reaching out to Microsoft Q&A forum.

I understand that you're dealing with a persistent and challenging issue, especially since you've already exhausted the common client-side troubleshooting steps (clearing cache, resetting credentials, and reinstalling). The fact that the issue is isolated to her laptop but persists after a full reinstall and sign-out suggests that the problem lies either in a deep local profile setting that the reinstall missed or in a specific OneDrive/SharePoint permission conflict tied to her user ID on the backend.

To help narrow down the root cause and determine whether this needs backend administrator intervention, please have the user attempt the file-sharing process again and note exactly what happens at each step.

• In a 1:1 or Group Chat: Does the user click the plus icon (+) (Action and apps) > Attach file and then the list of files fails to load? Or does the user try to upload a file from their computer, and a progress bar appears and then stalls/fails?
• In a Team Channel: Does the user try to upload a file to the Files tab, and receive a specific error message? (e.g., "Upload blocked," "You don't have permission to upload," or "The file couldn't be uploaded to the document library.")
• Does she see a "Loading..." message that never resolves, or a blank window?
• What happens in the web browser? Ask the user to log into Teams via the web browser. Try uploading a file in the browser-based Teams. Does it work there?
• What type of file are the user trying to share (e.g., Word, PDF, image)?
• Are they sharing it with an internal user or an external guest?
• If the user receives an error message, or sees a specific failure state (like a blank loading window), can she provide a screenshot of the issue? This visual evidence is extremely helpful for confirming the exact point of failure. IMPORTANT: Please ensure she masks or obscures any sensitive personal information before sharing.

If the file sharing works perfectly in the web browser, the problem is definitely isolated to the configuration or synchronization on the laptop's desktop client. If it fails in the browser too, the issue is a deep SharePoint/OneDrive permission failure tied to her user ID on the backend, which requires immediate M365 Admin intervention.

In the meantime, these steps target deep local profile and sync errors that a standard reinstall often misses:

Reset OneDrive Sync Status: Since Teams file sharing relies on OneDrive/SharePoint, resetting the OneDrive client on the user's laptop can sometimes clear sync errors that block sharing.

1. Close Teams and OneDrive.
2. Open the Run dialog (Windows Key + R).
3. Paste the command: %localappdata%\Microsoft\OneDrive\onedrive.exe /reset and press Enter.
4. The OneDrive icon should reappear in the taskbar. If it doesn't, manually restart it.

For reference: Reset OneDrive - Microsoft Support

Create a New Local Windows Profile: If the issue is a deeply corrupted operating system profile (which caches network credentials and system settings), a fresh start is necessary. Have the user log into the laptop using a new temporary Windows user profile. If Teams works perfectly under the new profile, the original Windows profile is the source of the issue.

If none of the above solutions work, let me know in the comments for further investigation. Please note that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution. Thank you for your patience and understanding. I'm looking forward to your reply. 

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