We recently lost our ability to log in to our ClearPass subscriber, and also found that it's not processing TACACS+ logins (both for itself and for our routers that are configured to use it). We're on version 6.6.2, and our publisher is working fine. I've tried restarting the TACACS service on the subscriber, and rebooting the subscriber, but no luck.
When I tried to log in to the subscriber, I could see the attached error in the logs on the publisher. Interestingly enough, when I came in this morning, it suddenly seems to be working again.