You point MCA Selector at a world and it crashes, freezes, or hangs while loading — sometimes before the map even appears. The best-known report of this is issue #299, where a 1.17.1-era tool froze trying to load a 1.18 world, and the pattern behind it still explains most cases today.
The main cause: the tool is older than the world
Minecraft’s world format evolves with every game update, and MCA Selector has to be updated to understand each new one. The support window is defined by DataVersion: the current MCA Selector 2.9 covers worlds up to Minecraft 26.3 (DataVersion 5023+), but an older tool build simply cannot parse chunks written by a newer game — and failing to parse them can mean a freeze or a crash rather than a tidy error message. Our DataVersion list shows which values belong to which game version, and our version history shows which MCA Selector release added support for what.
Fix it step by step
- Check your MCA Selector version (title bar / About) against the current release. If your world was last saved by a recent Minecraft version, update MCA Selector first — for 26.x worlds you need the 2.7+ line, and for 26.3 worlds you need 2.9.
- Close Minecraft completely before opening the world in MCA Selector; a world that is open in the game (or on a running server) is mid-flight and not safe to read or edit.
- Try opening a different, freshly created world. If that loads fine, your installation is healthy and the problem is specific to the first save; if every world crashes the tool, suspect the installation or its Java runtime instead (see our not-opening guide).
- If one specific world fails while others load, work on a copy of it: restore its region files from your most recent backup into the copy and test again. A world that used to load and suddenly does not, where only some saves are affected, is the basic fingerprint of damaged files in that save — the backup copy is the fix, not a repair utility.
A special case: snapshot worlds
If the world was played in a Minecraft snapshot, temper your expectations: the official README states plainly that there is no guarantee snapshot worlds work and that old snapshots are not supported. Snapshot formats can change between weekly builds in ways no external tool can fully track. Your realistic options are to wait for (or update to) an MCA Selector release that catches up, or to edit the world after it has been opened and re-saved by the matching release version of Minecraft.
If it still does not work
Launch the tool from a command line (java -jar mcaselector-2.9.jar) and open the world again — the stack trace printed when it fails is exactly what the upstream tracker needs. Search the Querz/mcaselector issues for your MCA Selector version plus your world’s Minecraft version before posting, and include the trace, both version numbers, and whether other worlds load.
Get the Current Version First
Several of the problems in this guide disappear on the current release. MCA Selector 2.9 is free and open source — get the Windows installer, the cross-platform .jar, the macOS .dmg or the Linux .deb/.rpm from the MCA Selector download page, where every button points at the official GitHub release files with their SHA-256 checksums.
More troubleshooting
This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.