Just a quick update to this. Point number 2 in the comment by mmorales above was actually the issue. The server side config was correct (which is what I was checking), but the client side config was not.
Apparently, the older clients would work despite being set to explicitonly in the console.exe.config file, but the 7.7.1 version has some additional authentication changes that caused it not to work unless that key was correct.
Eric