Guacamole Client Incompatible? - Stack Overflow

About a month ago, I inadvertently trashed my VM running Guacamole. It had been up for at least a year, maybe two. I've been trying to rebuild it, using the article I had in my notes as how I did it in the first place, cross-referencing the official docs. It doesn't work. Just trying to get to the front page fails, with the following message in syslog:

guacd[36987]: ERROR:#011Guacamole protocol violation. Perhaps the version of guacamole-client is incompatible with this version of guacd?

No other log is particularly helpful.

How it's set/things I've tried:

• First attempt at OS is Ubuntu 24.10, but I've since been trying 20.04.
• My first cut was Tomcat10, before I realized it had to be Tomcat9
• I've downloaded Guacamole from the Apache site. I originally did version 1.5.5, the latest, but tried 1.4.0, to match the instructions/what I had earlier.
• "Bad Gateway" when I try externally. Using an local browser pointed at 127.0.0.1:4822 gets ERR_EMPTY_RESPONSE on the browser, and kicks the above into the log.

Googling the specific message didn't give specific suggestions, though I did try them:

• Taking IPv6 out of the hosts file
• Substituting 127.0.0.1 for localhost/0.0.0.0
• Taking MariaDB out of the loop, just to see if that's the cause
• Read articles about Docker-based implementations, but they didn't seem relevant (as I'm not using Docker)

I've hit a point of frustration on this. Any suggestions for what else to check/different instructions/other?