Vincent, the package-reporter process runs as the "landscape" user and it doesn't have permissions to read that file.
We will probably address this problem by making the reporter not crash, but it still won't be able to read that file, so whatever packages that repository pulls in (when the line is uncommented), landscape won't see them.
To workaround the crash, please change the file permissions or ownership so that the landscape user can read it. Since you are already using a group, maybe you can use filesystem acls, like this:
setfacl -m u:landscape:r /etc/apt/private-ppa.launchpad.net_commercial-ppa-uploaders_braid_ubuntu.list
Oh, ok, I see that you changed the permissions to 0644 already. I suppose the perms where set to 0640 before by the tool that added the file, since it looks like it contains a password.