What the message is telling you
You see this on the Server Workshop Items screen, which appears when you join a server and lists the Workshop items it requires. The Indie Stone's text files carry the full wording: the error is Workshop item version is different than the server's, and the detail underneath reads Possibly the server's version is outdated, requiring the server to be restarted. If your version is outdated, try restarting Steam to get the latest version.
The important word there is possibly. The game knows the two copies differ, and the message does not say which one is behind. A Workshop item can be updated by its author at any moment, and the two copies then move at different times. Steam brings a player's subscribed copy up to date, while a running server keeps the copy it loaded. So the error often appears out of nowhere on a server nobody has touched, right after a mod update.
The screen shows a state beside each item, which is your best clue to the one causing trouble.
- Not Subscribed: Steam has not subscribed you to this item yet
- Downloading: wait for it to finish
- Update Required: your copy is behind, so restart Steam
- Installed: your copy looks complete, so look at the server next
- Error: note the item's name or Workshop ID and work through the steps below
Work out which side is behind
Spend one minute on this before deleting anything, because it decides which fix you need. Ask the other players first. The pattern of who can join is the fastest evidence you have.
If you run the server, there is a direct check as well. The admin command checkModsNeedUpdate, which PZwiki describes as indicating whether a mod has been updated, writes its answer to the log file. The community script ZomboidScript looks for the line CheckModsNeedUpdate: Mods need update, so that is the text to search for in the server console log. The Change Notes tab on the item's Workshop page shows when its author last published, which you can compare with the server's last restart.
- Several players blocked, and the server has run for a while: the server is probably behind
- One player blocked and everyone else joins: that player's copy is probably behind
- Your item shows Update Required or Downloading: your copy is behind
- Your item shows Installed and the error stays after restarting Steam: suspect the server
- The item's change notes are dated after the server's last restart: the server needs a restart
Fix it on the server: a full restart
This is the fix the game itself suggests, and on a running community server it is the one you will use most. The server's settings text says it installs Workshop items when starting, so the update arrives when the process stops and starts again. Valve's documentation describes the same arrangement from its side: a game server is given the item IDs and downloads the items itself.
Stop the server with the quit command, which saves and then exits, and start it again. If players are online, warn them first with servermsg. Give it time to finish starting, since the Workshop downloads happen during startup, then try joining.
If the error survives a clean restart, established practice is to make the server fetch that item again. Stop the server, back up, delete only the folder named after the item's Workshop ID, and start up. On a server install the folder is normally steamapps/workshop/content/108600/ followed by the ID, inside the server's install folder. Deleting the item's folder removes downloaded mod files and leaves your world alone, and a backup of the Zomboid folder covers you either way.
- Warn players: servermsg "Restarting for a mod update"
- Stop cleanly with quit, so the world saves before the process ends
- Start the server and wait for it to finish starting
- Still failing: stop, back up, delete the one item's folder, and start again
- Check that item's number is still listed on the WorkshopItems line in servertest.ini
Fix it on your own PC: Steam first
If you are the one player who cannot join, work through this list in order. It moves from harmless to thorough, and each step is worth trying before the next. Restarting Steam comes from the game's own message. Valve's documentation explains why it helps: when a game launches, Steam updates any installed Workshop items that need it before it starts the game. The later steps are what players report working in the Steam discussions, so treat them as community practice.
The last step costs you a full download of every Zomboid mod you own, which is why it sits at the end. Your saves stay in the separate Zomboid folder in your user directory, and it is still sensible to copy that folder first.
- Close the game, exit Steam completely, and open it again
- Open Steam's Downloads page and let any Project Zomboid Workshop updates finish before launching
- Unsubscribe from the failing item, resubscribe, and wait for it to download
- Still failing: exit Steam and delete that item's folder in steamapps\workshop\content\108600, named after its Workshop ID
- Last resort: exit Steam, delete the whole 108600 folder and appworkshop_108600.acf from steamapps\workshop, then resubscribe
If you host from inside the game
Hosting with the Host button in the main menu adds a twist, because your game and your server can each hold a copy of the mods. Players in the Steam discussions report the server's copy sitting inside the game's own install folder, at steamapps\common\ProjectZomboid\steamapps\workshop, separate from Steam's main steamapps\workshop folder. That means you can see this error on your own server, with both copies on one PC.
The fix those players report is to close the game and Steam, delete the old item folders under content\108600 in the game's own workshop folder, and let them download again. Those reports go back several years, so check the path on your own machine before relying on it. If the folder is not there, your game keeps its copy elsewhere and the steps in the earlier sections apply.
A dedicated server avoids this overlap, since it runs from its own folder. The Project Zomboid dedicated server setup guide covers installing one, and self-hosting vs renting weighs up the options.
Similar errors with different fixes
Restarting for a mod update will not help if your problem is a different mismatch. Read the wording closely, because these messages sit close together and each one has its own fix.
The most common neighbour is a game version mismatch. Its text reads Client version, then a number, does not match server version, then a number. That is about the game itself, and it means you and the server are on different builds or Steam branches. As of 31 October 2026 the Stable branch is 42.21 and the Pre-Release branch, which replaced the name Unstable, is 42.22. The dedicated server, app 380870, also has legacy41 and 42.19 branches. The Indie Stone plans to keep each build on Pre-Release for at least one week before it moves to Stable, so check the numbers again when an update lands. Everyone has to be on the same version, and the server updates with the same command it was installed with.
The other one is a kick with the text You have been kicked because your game files do not match the server's. That comes from the DoLuaChecksum setting, and it is on by default. PZwiki advises keeping it on for security, and it also warns of a bug that can flag false positives on Linux servers, so verify your game files and compare mod lists before you consider turning it off.
- Workshop item version is different than the server's: one mod's copies differ
- Client version does not match server version: the game builds differ
- Your game files do not match the server's: the DoLuaChecksum check failed
- Update the server: app_update 380870 validate in SteamCMD, stable branch by default
- Join a Pre-Release server: choose Pre-Release under Game Versions & Betas in the game's Steam properties
Keep it from coming back
You cannot stop mod authors publishing updates, and the longer a server runs, the more likely one lands while it is up. The practical answer is to make restarts routine. A daily restart at a quiet hour brings every Workshop item up to date, so a mismatch lasts only until that restart and players learn when to expect it.
For larger mod lists, admins automate the check. They send checkModsNeedUpdate over RCON on a timer, search the log for the Mods need update line, warn players, and restart when it appears. ZomboidScript is one public example, and it restarts straight away when nobody is online. Its author notes that the command's answer goes to the log and does not come back over RCON, which is why the log has to be read.
A shorter mod list also helps, since every item is one more thing that can update mid-session. Keep the list on the two lines where it belongs: WorkshopItems holds the Workshop numbers and Mods holds the mod IDs. Before a restart that pulls in a large mod update, make sure you have a backup. BackupsOnStart is on by default, and our setup guide lists what else is in the Zomboid folder worth saving.
- Restart on a schedule, with a servermsg warning first
- Automate checkModsNeedUpdate if your mod list changes often
- Keep a backup before any restart that brings in a large mod update
- Tell players to restart Steam if the error appears right after a mod update