Generator Won't Run on 1.17.1 world - "SEVERE: Invalid level format."

[EvilSupahFly]

So, I have a server being setup for my kids and their friends. Naturally, I figured I would pre-generate a large chunk of the terrain, so I came here, as I have in previous years.

The problem is now, with a vanilla 1.17.1 server, I only get errors when trying to run MLG. To start, I loaded the server from the terminal, then I logged in, set the world spawn, and logged out, figuring that should be enough to get MLG started with:

[14:07:24 INFO]: EvilSupahFly joined the game
[14:07:24 INFO]: EvilSupahFly[/127.0.0.1:35876] logged in with entity id 546 at ([SMP Of The Bee]224.5, 146.0, -223.5)
[14:07:57 INFO]: EvilSupahFly issued server command: /gamemode creative
[14:07:57 INFO]: [EvilSupahFly: Set own game mode to Creative Mode]
[14:09:57 INFO]: EvilSupahFly issued server command: /setworldspawn
[14:09:57 INFO]: [EvilSupahFly: Set the world spawn point to 379, 68, -113 [0.0]]
[14:11:30 INFO]: EvilSupahFly lost connection: Disconnected
[14:11:30 INFO]: EvilSupahFly left the game

Then I loaded MLG with basic starting instructions, but it fails every time. The first time, I got this:

evilsupahfly on black-beast Sun Dec 05 02:19 PM
[~/mc_server] $ java -jar MinecraftLandGenerator.jar 2000 2000 -i200 -x379 -z-113
[MLG] Minecraft Land Generator version 1.7.6
[MLG] BuildID: (1421666774000)
[MLG] This version was last modified on Monday, January 19, 2015 at 6:26 AM, Eastern Standard Time
[MLG] 
[MLG] Uses a Minecraft server to generate square land of a specified size.
[MLG] 
[MLG] 
[MLG] Notice: Non-Default Increment: 200
[MLG] Notice: X Offset: 379
[MLG] Notice: Z Offset: -113
[MLG] Processing world "./SMP Of The Bee", in 200 block increments, with: java -Djava.awt.headless=true -Djline.terminal=jline.UnsupportedTerminal -Duser.language=en -Xms1024m -Xmx1024m -Xincgc -jar server.jar nogui
[MLG] 
[MLG] 
[MLG] Backing up level.dat to level_backup.dat.
[MLG] 
Dec. 05, 2021 2:24:20 P.M. morlok8k.MinecraftLandGenerator.Main runCLI
SEVERE: Invalid level format.
java.io.IOException: Invalid level format.
	at morlok8k.MinecraftLandGenerator.SpawnPoint.getSpawn(SpawnPoint.java:77)
	at morlok8k.MinecraftLandGenerator.Main.runCLI(Main.java:207)
	at morlok8k.MinecraftLandGenerator.Main.main(Main.java:132)

evilsupahfly on black-beast Sun Dec 05 02:24 PM
[~/mc_server] $ 

On all subsequent attempts, there's two extra lines in the terminal, which makes sense, given the initial failure:

[MLG-ERROR] There is a level_backup.dat file left over from a previous attempt that failed.
[MLG] Resuming...

Does MLG not work with newer versions of Minecraft?