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RLCraft reports “server mod rejections” when the client and server do not agree on the modpack identity, Forge loader, mod jars, dependencies, or a mod’s network handshake. The dependable fix is to make both sides match the same RLCraft release, Minecraft 1.12.2, Forge build, and mod files, starting from the official client and server packs. Then use the named mod in the rejection as your diagnostic lead rather than changing unrelated files.
What a server mod rejection means
Forge checks a connecting client before allowing it into a modded server. It compares the mod metadata and network-handshake behavior expected by the server with what the client presents. A rejection therefore usually indicates a mismatch, not a problem with your world or internet connection.
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For RLCraft, the baseline is especially specific. The official project is a Forge modpack for Minecraft 1.12.2. Its listed v2.9.3 release has a corresponding server pack. The project states that RLCraft v2.9 “comes with and requires Forge 2860,” packaged as Forge 1.12.2-14.23.5.2860. Treat that as the starting point for the v2.9.x line and verify the exact pack file you installed before trying another Forge build.
A rejection may identify a particular mod, version, or handler. That text is the most useful clue: it tells you where the client-server contract first failed. Read the complete rejection screen and the latest server log before deleting or updating anything.
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Use the right RLCraft files first
The official release listing provides two different archives:
| Purpose | Official file listed for v2.9.3 | What it supplies |
|---|---|---|
| Client | RLCraft 1.12.2 – Release v2.9.3.zip | The client-side modpack files and configuration |
| Dedicated server | RLCraft Server Pack 1.12.2 – Release v2.9.3.zip | The server installation files and configuration |
Do not build a server by copying a few visible client mods into an unrelated Forge installation. Start with the matching server-pack archive, and use the matching client release for players. If you installed an older RLCraft release, every player must use that same release; a v2.9.3 client cannot be assumed compatible with a different pack revision.
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- Save the complete rejection text. Record every named mod, version number, and phrase such as
Failed mod's custom NetworkCheckHandler. - Copy the latest server log. Keep the log from the failed connection, not an earlier startup. Note the Minecraft version, Forge version, and the first error involving the rejection.
- Record both installations. Write down the RLCraft release, Forge build, and the filenames in each
modsdirectory. Include file versions where the filename provides them. - Stop the server before editing. Shut it down cleanly so that configuration and log changes are written and no jar is locked while you replace it.
Do not diagnose from a shortened screenshot when the server log contains the full exception. A mod can appear in the final rejection even though an earlier dependency or duplicate caused the initial failure.
Check the four identities that must match
RLCraft release
Both sides must use the same release archive. Confirm that the launcher profile and the server directory are both based on the intended release, such as v2.9.3. Mixing a newer client with an older server pack changes more than the visible mod list: configuration files, dependency versions, and pack-specific patches can differ.
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Minecraft version
RLCraft’s official pack is for Minecraft 1.12.2. A Forge installation for another Minecraft version cannot load the pack correctly, even if a mod has a similarly named jar available for that version.
Forge loader and build
For the v2.9 baseline, verify Forge 1.12.2-14.23.5.2860, the build the project identifies for RLCraft v2.9. Do not “upgrade” Forge as a first response. A different build can alter loader behavior and make a previously accepted jar fail. If you deliberately use another build, establish that the exact RLCraft release and every installed mod support it; otherwise return to the pack’s stated build.
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Mod jars
The client and server need the same required mod versions and compatible metadata. Compare the actual jar filenames, not just the number of files. A file with the same mod name but a different build is still a mismatch. Remove an old jar when installing its replacement; leaving both copies creates a duplicate-mod failure.
Cleanly reinstall the server pack
A clean installation is often faster than trying to repair a directory that has accumulated old jars and configuration files.
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- Create a new, empty server directory and back up the existing world,
server.properties, whitelist, operator list, and any scripts you need to preserve. - Extract the official RLCraft server-pack archive into the new directory.
- Install or use the Forge version required by that pack. Confirm that the startup output reports Minecraft 1.12.2 and the expected Forge 14.23.5.2860 baseline.
- Accept the EULA when the server creates
eula.txt, then stop the server before copying personal data back. - Copy the world and carefully reapply server-specific settings. Do not overwrite the pack’s
modsorconfigdirectories with folders from the old installation. - Start the server, let it finish loading, and test with a client made from the matching RLCraft release.
For a manual setup, the official instructions say to make sure there is nothing in the Mods or Config folders before copying those folders from the modpack. The capitalization shown by the instructions may differ from your operating system’s display, but the important point is to empty the existing folders first. Otherwise stale jars and settings remain alongside the pack’s files.
Compare the client and server mod directories
After confirming the release and loader, compare both sides one jar at a time. Make a two-column inventory with the exact filename, version, and whether the jar is present on the client, server, or both.
| Finding | Corrective action |
|---|---|
| Same mod appears twice on one side | Keep the single jar required by the pack and remove the duplicate, then restart. |
| Required jar exists on only one side | Install the matching pack version on the missing side, including its dependencies. |
| Client-only performance or graphics jar is on the server | Remove it from the server while testing; add it only if the pack explicitly supports server loading. |
| Jar targets another Minecraft version or loader | Replace it with a Forge 1.12.2 build compatible with the RLCraft release. |
| Filename differs only by a version number | Use the same build on both sides; do not leave the older jar beside the newer one. |
| Dependency is absent or invalid | Restore the dependency from the matching pack or obtain the exact compatible dependency version. |
CurseForge’s support guidance identifies duplicate mods, missing or invalid manifest references, wrong modloaders, and missing dependencies as common rejection causes. In a manually installed server, those checks translate directly into the inventory above. A file can also be rejected when its author’s loader tag does not identify it as compatible, even if the jar name looks plausible.
When a named mod appears in the rejection
Do not replace every mod at once. Isolate the named jar and check its exact build, dependencies, and loader target. The safest change is normally to replace that one jar with the version supplied by the matching pack, or roll it back to the last compatible build, on both the client and server.
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LootTweaker and NetworkCheckHandler
A documented RLCraft case from January 15, 2022 reported:
LootTweaker: Failed mod's custom NetworkCheckHandler FMLMod:loottweaker{0,3,1}The response recommended downgrading LootTweaker and replacing it on both server and client. This is a case-specific remedy, not a promise that every LootTweaker rejection requires the same version. Use the version shown in your own log and the pack’s known-compatible file. After replacing it, remove the old jar, restart the server, and test with a clean client profile.
Other named mods
For any other mod, follow the same sequence:
- Record the mod ID and version exactly as printed by Forge.
- Check whether the jar is a Forge 1.12.2 build and whether its dependencies are present.
- Compare the client and server copies byte-for-byte in practical terms: same filename and build, with no second copy.
- Replace or roll back only that mod on both sides.
- Restart and read the new log. If the named mod changes, begin the process again with the newly identified failure rather than restoring unrelated updates.
Remove optional additions while isolating the problem
Optional graphics and performance additions can obscure the real mismatch. The official RLCraft instructions specifically warn: “Do NOT use E3 Optifine anymore as this will crash.” They recommend the 1.12.2 G5 OptiFine build instead, and identify VanillaFix and BetterFPS as incompatible with RLCraft.
Temporarily remove E3 OptiFine, VanillaFix, BetterFPS, and any other mod you added outside the official pack while testing. Keep a backup of those jars so you can restore only versions explicitly compatible with the pack after the server and a clean client connect successfully. Do not put a client-only graphics jar into the dedicated server directory simply because it is present in a client profile.
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Check dependencies and loader compatibility
A mod rejection can be a symptom of an earlier load failure. Inspect the server log for “missing dependency,” “invalid mod,” “wrong modloader,” or a required version range before the final network message. CurseForge explains that a loader warning commonly means the mod is not compatible with the modpack’s loader, or that an update removed support for a loader version that previously worked. Its prescribed remedy is to update to a compatible version or roll back to a version that works with the installed loader.
- Use a Forge 1.12.2 jar, not a Fabric, Quilt, or newer Forge build.
- Check the mod’s required libraries and their versions.
- Install dependencies on the side where they are required; do not assume a client-only library belongs on the server.
- Undo recent “latest version” updates when the rejection began immediately afterward.
- Do not keep two releases of the same dependency in the directory.
Verify server.properties and restart behavior
RLCraft’s official instructions require enable-command-block=true in server.properties. This setting is not usually the direct cause of a mod-list rejection, but leaving it disabled can prevent some structures from generating correctly and may leave villagers missing. Set it deliberately, save the file, and restart the server; do not expect a running process to adopt the change.
After every jar or configuration change, perform a full stop and start. A reload command does not replace a Forge restart, and an old process can continue using the previous classpath.
Use a clean-client test to separate server and client faults
- Make a fresh launcher profile from the same RLCraft release as the server.
- Do not copy optional shaders, performance mods, or custom jars into that profile.
- Confirm its Minecraft and Forge versions match the server’s startup log.
- Connect once and save the complete result.
- If the clean profile works, add personal client additions one at a time until the incompatible file is identified.
If a clean client still receives the rejection, compare its mod inventory with the server again and inspect the server log for the first dependency or loader error. If only a customized client fails, the server pack is less likely to be at fault than the additional client jar or configuration.
Common fixes that make the problem worse
- Updating everything at once: You lose the named-mod clue and may introduce several new incompatibilities.
- Changing Forge without matching the pack: The RLCraft v2.9 baseline is Forge 14.23.5.2860; changing it is not a neutral repair.
- Leaving old jars in place: A replacement does not help if the original jar remains and Forge loads both.
- Copying the entire old Mods or Config folder back: This reintroduces the stale files a clean installation was meant to remove.
- Putting every client mod on the server: Graphics, optimization, and other client-only additions can fail during server loading.
- Trusting a shortened error: The final line may hide a missing dependency or earlier loader exception.
- Testing with a heavily customized client: A clean profile is needed to establish a reliable baseline.
A practical decision path
| What you observe | Next action |
|---|---|
| Different RLCraft, Minecraft, or Forge versions | Install the same official release and Forge baseline on both sides. |
| Duplicate filename or two builds of one mod | Remove the stale copy and restart. |
| Named mod with a NetworkCheckHandler failure | Use the exact log version, then replace or roll back that jar on client and server. |
| Missing dependency or invalid manifest reference | Restore the dependency from the matching pack and remove unrelated updates. |
| Wrong-loader or incompatible optional mod | Remove it; install only a Forge 1.12.2-compatible version. |
| Everything matches but rejection persists | Rebuild from the official server pack, test with a clean client, and preserve the new log for support. |
What to include when asking for support
Provide the exact RLCraft release, Minecraft version, Forge build, complete rejection text, named mod and version, the server’s latest log, and a list of any files added outside the official pack. State whether the server was rebuilt from the official server pack and whether a clean client was tested. Support guidance is much more useful when it includes the exact rejection message and the submitted file rather than a description such as “mods don’t match.”
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