MRPack to ZIP

Loader Version Mismatch — Fixing Crashes After Importing a ZIP

Symptom

Minecraft crashes during the loading screen with errors like java.lang.NoClassDefFoundError or Mixin apply failed. The launcher log mentions Fabric or Forge.

Cause

The instance is running a mod loader version older or newer than the modpack expects. Most mods are sensitive to even minor version drift in the loader.

Fix

  1. Find the required loader version

    It is in the converter's progress log under "Dependencies." Example: Fabric Loader 0.15.6, Forge 47.2.0.

  2. Match it in your launcher

    In CurseForge, Prism, MultiMC, or ATLauncher, open instance settings → loader → pick the exact version.

  3. Re-launch

    The crash should be gone.

If you cannot find the exact version

Mod loaders are very forwards-compatible — a slightly newer version usually works. Avoid older versions, which lack required APIs.