Online Servers Mod Mismatch Errors What They Mean in Assetto Corsa
admin
AC Supply Team
You join a lobby and get bounced with a mod mismatch or checksum error. The game does not always explain whether you are missing a file, have a newer car than the server, or simply pointed at the wrong content pack. This article translates those failures into action.
Pair it with our install guides and browse when you need to source specific builds.
Servers enforce consistency for a reason
Multiplayer assumes every client loads the same physics data and collision meshes. If one player sneaks a lighter car model or different tyre file, competition breaks. Checksums are the blunt instrument that enforces fairness—even when they feel annoying.
Newer is not automatically compatible
Players assume “I have the latest, so I am good.” Servers often pin older stable builds for a season. Your v2.1 car may fail against a v2.0 checksum. Read the league sheet literally.
Skin-only differences can still matter
Some servers checksum entire folders; others ignore skins. If you are rejected after adding a livery, ask admins whether skins are whitelisted or if you accidentally changed a data file while painting.
Apps and CSP injections
Certain plugins or CSP features alter memory layouts or shaders. Private servers may require a specific CSP range or ban injectors outright. If rules mention “no extra apps,” believe them before you argue in chat.
Fixing mismatch methodically
- Remove the listed car or track folder entirely.
- Install the exact archive the league distributes—hash or filename match if provided.
- Restart Content Manager and let it rescan.
- Rejoin with minimal overlays for the test.
If you still fail, compare file sizes against a teammate who connects successfully.
Log files admins may ask for
Some communities collect server-side rejection logs that name exact mismatched filenames. If an admin posts a path like data.acd or a specific kn5, believe the precision—do not argue with “but it works offline.” Offline has no checksum gate.
Practice servers versus race servers
Leagues often run lower-security practice rooms and strict race rooms. Passing practice does not prove race readiness if checksum modes differ—read the announcement footer every week.
VPN and region routing (edge case)
Rarely, packet loss masquerades as timeout kicks after mod sync. If you pass checksum but disconnect instantly, test wired networking before you reinstall mods for hours.
FAQ
Can I hotfix myself?
Only if admins allow; unsanctioned edits risk bans.
Do public lobbies differ?
Yes—rules are looser but errors are vaguer.
Where do I get pinned versions?
League discords, AC Supply listings with version notes, or author pages.
Mismatch errors are gatekeepers, not insults. Align versions, respect stewards, and you are back on grid.
If admins publish a torrent or sync tool, prefer that over manual hunting—humans mis-click filenames more often than torrent clients corrupt data.
Teach teammates to zip their working folder tree with version in the filename when sharing internally; your future self thanks you at 11:58 p.m. grid time.
Small naming discipline prevents entire divisions from scrambling five minutes before formation lap.