You may get this screen while you are using a beta/snapshot, or after Aristois has an update. To fix it, you can manually delete the EMC.jar.
Note: This message is intentional on beta and snapshots, as it's an irregular version. You cannot fix it, but you can press Esc or Continue to bypass it.
1. Close the game and go to your
2. Then go to
3. Delete the
4. Start the game as normal.
If it didn't work, make sure all Minecraft windows (games & launcher) have been closed first, and retry, or contact staff.