Troubleshoot adding files

When I try to add a file to Perforce Helix Server, I get an error stating that the file is not "under client's root." What does this mean?

To add a file to Perforce Helix Server successfully, the file must be saved in your client workspace Directories on your machine where you work on file revisions that are managed by Helix Core Server. By default, this name is set to the name of the machine on which your client workspace is located, but it can be overridden. Client workspaces, labels, and branch specifications cannot share the same name.. If you do not know what this means, see your Perforce Helix Server administrator.