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How to FIX Microsoft Teams File Unknown Error

You can share files over Microsoft Teams which is standard for most chat applications. What sets Microsoft Teams apart though is that Microsoft 365 apps are integrated with it. If a Microsoft 365 file has been shared in Microsoft Teams, users will be able to open it within Microsoft Teams, and edit and collaborate on it.

Fix: Microsoft Teams file unknown error

When accessing files shared with a team in Microsoft Teams, users sometimes see the ‘File Unknown’ error. The file does not open, not even in a preview and the user is unable to edit it. The error isn’t specific to files that were created in a Microsoft 365 app. It can appear for just about any type of file.

1. Download and open file

It is possible that the file has been corrupted. It may have been corrupt when it was uploaded or too many users accessing/editing it may have caused a problem when the changes were saved. Check if you can open the file outside of Microsoft Teams.

  1. Open Microsoft Teams.
  2. Select the Team/chat thread the file was shared to.
  3. Go to the Files tab.
  4. Select the file.
  5. Click Download.
  6. Once downloaded, open the file on your desktop. If it doesn’t open, it is likely corrupt and you need to restore it or find a copy that isn’t corrupt.

2. Open in browser

Try opening the file online. This can help resolve the Unknown error if the file won’t open due to a permissions conflict.

  1. Open Microsoft Teams.
  2. Go to the Team/conversation the file has been shared over.
  3. Click the more options (three dots) button next to the file.
  4. Select ‘Open in browser’.
  5. A new tab will open in your default browser.
  6. Sign in with your Microsoft Teams account and see if you’re able to access the file.

3. Log out and log back in

Some users only see the Unknown error when they try to access the file in Microsoft Teams (desktop and/or web version). The file opens in mobile apps just fine. In that case, try signing out and signing back into Microsoft Teams.

  1. Click your profile icon at the top right.
  2. Select Sign out.
  3. Quit Microsoft Teams; right-click the app’s icon in the system tray, and select Quit.
  4. Open Microsoft Teams again.
  5. Sign in, and access the file.

4. Edit channel name

Files can be uploaded to and shared from a SharePoint folder and they show up in Microsoft Teams like any other shared file. When a file from SharePoint is uploaded to a channel, a folder with the same name as the channel is created in SharePoint. While the channels can be renamed, the folders in SharePoint cannot be renamed. If you’ve changed the name of a channel it will no longer match that of the SharePoint folder, resulting in this error. You will have to change it back.

Note: this fix is only for users who have SharePoint configured.

  1. Open Microsoft Teams.
  2. Select the Team with the folder error.
  3. Select General under the team.
  4. Go to the Files tab.
  5. Click ‘Open in SharePoint’.
  6. Go to the root of the SharePoint and note down the name of all the folders.
  7. Return to Microsoft Teams.
  8. Select the team with the folder error.
  9. Examine all the channels under it, and make sure the name matches that of the folders you noted.
  10. If a name doesn’t match, click the more options (three dots) button next to a channel, and select Edit this channel.
  11. Change the channel name to match the folder name in SharePoint.
  12. Log out, and log back into Microsoft Teams.
  13. The document will now be accessible. 


If a file will not open in Microsoft Teams, you will have trouble collaborating on it but, your file isn’t lost. It is rare that a file is lost or corrupted simply because it was shared over Microsoft Teams. SharePoint may complicate accessing some files but for the most part, they’re safe and will open.

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