Make sure that the Primary AIM is not set to "Require SSL for Web" (under network settings) when adding backup/satellite AIM Managers as it will fail to be added. The redundant_procs file which is part of the setup is not available on an HTTPS connection. You can revert to using an HTTPS connection after the AIM's have they have synchronised, but just remember to unset it again if you need to replace an AIM. Known to affect all AIM's running 4.7 and below.