Problem with attaching files in Teams chat or channel

 Error:

 When user is trying to upload files using MS Teams for a channel, getting files are locked error.

Cause :

The user does not have corresponding MSTeams channel site access.

Note: Every MS Teams channel has its own SharePoint sites. So when we upload files in MS Teams it will upload in SharePoint. So the affected users can verify themselves whether they have correct permission to access the MSTeams channel site access , click POSTS tab then  three dots (...) --> Open in SharePoint option. 

Solution:

Check respective MSTeams channel's SharePoint site permission for the user and assign required permission for the user.