Free MS Teams Files missing March 2022

[RobDInstRE]

Hello,

We are a Charity using a free Outlook providing Teams.

We have trusted MS Teams and loaded files and folders into Teams for our volunteers to access and discuss.  These files have suddenly disappeared and I cannot find a solution.  This same discussion thread started quite strangely at this time last year.  How can I get back files when I am told 'The specified list is invalid'

[#2]

@RobDInstRE If from the post tab you press the ... on the far right and choose open in SharePoint do you get a more meaningful error.

It would seem most likely to me that someone has changed the permissions for the site where the Teams files are stored, and your account no longer has access.