3 managed devices but error message

sfman

I have a free TV account with 3 managed devices, which seems to be within the limit. I presume I can remote access (unattended) one from another without any problem. But when I tried to do this, the connection was ended after a few minutes with some message like reaching limit or not for commercial use. Also more seriously, somehow all three TVs are logged out, when I tried to re-login on any device, it always gave this error message. What's wrong here?