Removing Spell Effects from a player.dat file using NBTExplorer

If you recently upgraded your Yogscast Complete modpack to version 2.9.2.3-RR-YOGS the players re-joining the server may find that their client is crashing, or worse, the server is crashing because of data held in their player.dat file.

The cause is a change in the Potion IDs that have been set for the Ars Magica 2 mod. Players who logged out before the update with a status effect applied to their character will have invalid data in their player.dat file. At worst this will cause a crash, at best the status effect may change to a different status effect.

The easiest fix is to simply delete the player.dat file but you can remove just the status effects using the NBTExplorer tool:

http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-tools/1262665-nbtexplorer-nbt-editor-for-windows-and-mac

1. Run NBTExplorer
2. Choose File>>Open or click the 'Open' icon
3. Choose the player.dat file (it's located on the server at /world/players/<player-name.dat>)
4. Find the 'Active Effects' node and open it (Double-click or click the expand icon)
5. Inside will be the data for each active status effect, click on one to highlight it and press the delete key (or click on the delete icon)
6. Once all the Active Effects have been removed, choose File>Save or click the 'Save' icon