Hi Adelina,
I'm Amro, an Independent Microsoft advisor and a fellow Microsoft customer. I’m happy to look into this for you.
I understand that you are facing an Issue while trying to upload a file to a chat in Microsoft teams.
To start with basics, Please try to upload different file, if it works. then make sure the file you trying to upload is not damaged or is not on your hard disc (external memory disc for example)
If the error is with all files please check the following troubleshooting steps:
> Update MS Teams: https://support.microsoft.com/office/update-mic...
>> Please check the behavior with Teams Web App: https://teams.microsoft.com
>>> Clear Teams Caches:
- Quit Microsoft Teams. Right-click the icon and select Quit.
- Cut and paste %appdata%\Microsoft\Teams into File Explorer.
- Delete the contents of the entire folder.
- Restart Microsoft Teams.
https://learn.microsoft.com/microsoftteams/trou...
Check this thread discussing a similar Issue:
https://answers.microsoft.com/en-us/msteams/for...
I hope this helps, please feel free to reply to this if you need any further Assistance.
Kindly
Amro