Hello,
I have been migrating some company switches from RADIUS to TACACS+ authentication and authorization, and ran into the above error a few times. I could not find, quite literally, any information on this specific error but, I have now found the cause of the "expected packet type 61, got 50" error so I thought I would share how to fix it since it is unbelievably simple.
I use SecureCRT as my main SSH client for all of our switches, and while migrating the switches to TACACS+ authentication, I would sometimes get the error written in the title. Off of a pure guess, I wondered if my saved username had anything to do with this as the current switch I was working on had a saved username, and the one before did as well.
As soon as I deleted the username from the properties of the switch session stored in the left, I can successfully log in with every account included in the TACACS+ authorization profile.
Hopefully this works for some of you