Someone left the organisation but before leaving, he locked all the files for an unknown reason.
How do you unlock them all so that the other developers can work?>
For the following operation, you will need to be either a project administrator for the project you want to undo the check-in on or a Team Foundation Administrator if you want to do this across all projects.
If you still have the username of the person, you can simply do something like this:
tf lock /lock:none /workspace:WorkspaceName;USERNAME /recursive $/
To get the list of workspaces for a user, just run the following command from the same prompt:
tf workspaces /owner:username
For more commands, check tf /?