When a modded game refuses to start, the fix is almost always written in the log. This guide shows you where to look and matches the errors players most often hit with Cataclysm to their causes, then covers performance problems during big fights.
Step zero: read the log
Minecraft writes two useful files inside your game folder:
crash-reports/contains a report each time the game crashes. Open the newest one.logs/latest.logrecords the most recent launch, including errors that stop the game before a crash report is written.
Search for the first line containing ERROR, Exception or the word mod near a failure. The first error is usually the real one; later errors are often knock-on effects.
Common problems and fixes
"Missing or unsupported mandatory dependencies"
Forge lists the mod that is missing and the version range it wants. Install that library in a matching version. If it says the Minecraft or Forge version is wrong, your Cataclysm file was built for a different setup.
The mod doesn't appear in the Mods list
Usually one of three things: the jar is in the wrong instance's folder, you launched the vanilla profile instead of Forge, or the file in mods is the source ZIP from GitHub rather than a compiled jar. See building from source for the last case.
Two versions of the same mod
Updating by copying a new jar next to the old one gives Forge duplicates, and it stops with an error. Keep exactly one Cataclysm jar in the folder.
"Mismatched mod" when joining a server
The server and client must have the same Cataclysm version and the same dependencies. Ask the server owner for the exact file list.
Crash when entering a structure or starting a fight
This points to a conflict with another mod that touches entities, rendering or world generation. Test with only Cataclysm and its dependencies. If that works, add your other mods back in halves until the crash returns; that tells you which mod is involved.
Out of memory
Large modpacks need more memory than vanilla. In your launcher's profile settings, raise the maximum memory moderately (for example to 4–6 GB for a mid-size pack). Allocating nearly all of your system's RAM can make things worse.
Low FPS during boss fights
Boss arenas are large and full of effects. If frame rate drops during fights:
- Lower render distance a few steps; this has the biggest effect.
- Reduce particles to Decreased in video settings.
- Try the fight without shaders to see whether they are the bottleneck.
- Use a performance mod made for Forge in your Minecraft version, and test it on a copy of your world first.
Still stuck?
When you ask for help on a community forum or the project's issue tracker, include your Minecraft version, Forge version, Cataclysm file name, full mod list and the crash report. That turns a long back-and-forth into a quick answer. For general setup, the installation guide is a good reset point.
Want the bigger picture? Return to the Cataclysm Mod homepage or browse every guide.
