Try to use consistent UUIDs and not rely on Bukkit lookup while saving.

Essentials/src/com/earth2me/essentials/EssentialsUserConf.java

@@ -12,8 +12,8 @@ import org.bukkit.Bukkit;
 
 public class EssentialsUserConf extends EssentialsConf
 {
-	final String username;
+	public final String username;
-	final UUID uuid;
+	public final UUID uuid;
 
 	public EssentialsUserConf(final String username, final UUID uuid, final File configFile)
 	{

Essentials/src/com/earth2me/essentials/User.java

@@ -240,7 +240,7 @@ public class User extends UserData implements Comparable<User>, IReplyTo, net.es
 	{
 		if (!base.isOnline())
 		{
-			this.base = new OfflinePlayer(base.getUniqueId(), ess.getServer());
+			this.base = new OfflinePlayer(getConfigUUID(), ess.getServer());
 		}
 		cleanup();
 	}

Essentials/src/com/earth2me/essentials/UserData.java

@@ -50,7 +50,10 @@ public abstract class UserData extends PlayerExtension implements IConf
 	{
 		config.forceSave();
 		config.getFile().delete();
-		ess.getUserMap().removeUser(this.getBase().getName());
+		if (config.username != null)
+		{
+			ess.getUserMap().removeUser(config.username);
+		}
 	}
 
 	public final void cleanup()
@@ -838,7 +841,7 @@ public abstract class UserData extends PlayerExtension implements IConf
 		this.lastAccountName = lastAccountName;
 		config.setProperty("lastAccountName", lastAccountName);
 		config.save();
-		ess.getUserMap().trackUUID(base.getUniqueId(), lastAccountName);
+		ess.getUserMap().trackUUID(getConfigUUID(), lastAccountName);
 	}
 
 	public void setNPC(boolean set)
@@ -968,6 +971,11 @@ public abstract class UserData extends PlayerExtension implements IConf
 		return new HashMap<String, Object>();
 	}
 
+	public UUID getConfigUUID()
+	{
+		return config.uuid;
+	}
+
 	public void save()
 	{
 		config.save();

Essentials/src/com/earth2me/essentials/UserMap.java

@@ -29,7 +29,7 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 	private final transient ConcurrentSkipListMap<String, UUID> names = new ConcurrentSkipListMap<String, UUID>();
 	private final transient ConcurrentSkipListMap<UUID, ArrayList<String>> history = new ConcurrentSkipListMap<UUID, ArrayList<String>>();
 	private UUIDMap uuidMap;
-
+	
 	public UserMap(final IEssentials ess)
 	{
 		super();
@@ -39,7 +39,7 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 		//users = CacheBuilder.newBuilder().maximumSize(ess.getSettings().getMaxUserCacheCount()).softValues().removalListener(remListener).build(this);
 		users = CacheBuilder.newBuilder().maximumSize(ess.getSettings().getMaxUserCacheCount()).softValues().build(this);
 	}
-
+	
 	private void loadAllUsersAsync(final IEssentials ess)
 	{
 		ess.runTaskAsynchronously(new Runnable()
@@ -77,12 +77,12 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			}
 		});
 	}
-
+	
 	public boolean userExists(final UUID uuid)
 	{
 		return keys.contains(uuid);
 	}
-
+	
 	public User getUser(final String name)
 	{
 		try
@@ -109,7 +109,7 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			return null;
 		}
 	}
-
+	
 	public User getUser(final UUID uuid)
 	{
 		try
@@ -125,7 +125,7 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			return null;
 		}
 	}
-
+	
 	public void trackUUID(final UUID uuid, final String name)
 	{
 		if (uuid != null)
@@ -142,7 +142,7 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			}
 		}
 	}
-
+	
 	@Override
 	public User load(final String stringUUID) throws Exception
 	{
@@ -154,9 +154,9 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			trackUUID(uuid, user.getName());
 			return user;
 		}
-
+		
 		final File userFile = getUserFileFromID(uuid);
-
+		
 		if (userFile.exists())
 		{
 			player = new OfflinePlayer(uuid, ess.getServer());
@@ -165,24 +165,29 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 			trackUUID(uuid, user.getName());
 			return user;
 		}
-
+		
 		throw new Exception("User not found!");
 	}
-
+	
 	@Override
 	public void reloadConfig()
 	{
 		getUUIDMap().forceWriteUUIDMap();
 		loadAllUsersAsync(ess);
 	}
-
+	
 	public void invalidateAll()
 	{
 		users.invalidateAll();
 	}
-
+	
 	public void removeUser(final String name)
 	{
+		if (names == null)
+		{
+			ess.getLogger().warning("Name collection is null, cannot remove user.");
+			return;
+		}
 		UUID uuid = names.get(name);
 		if (uuid != null)
 		{
@@ -192,12 +197,12 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 		names.remove(name);
 		names.remove(StringUtil.safeString(name));
 	}
-
+	
 	public Set<UUID> getAllUniqueUsers()
 	{
 		return Collections.unmodifiableSet(keys.clone());
 	}
-
+	
 	public int getUniqueUsers()
 	{
 		return keys.size();
@@ -207,28 +212,28 @@ public class UserMap extends CacheLoader<String, User> implements IConf
 	{
 		return names;
 	}
-
+	
 	protected ConcurrentSkipListMap<UUID, ArrayList<String>> getHistory()
 	{
 		return history;
 	}
-
+	
 	public List<String> getUserHistory(final UUID uuid)
 	{
 		return history.get(uuid);
 	}
-
+	
 	public UUIDMap getUUIDMap()
 	{
 		return uuidMap;
 	}
-
+	
 	private File getUserFileFromID(final UUID uuid)
 	{
 		final File userFolder = new File(ess.getDataFolder(), "userdata");
 		return new File(userFolder, uuid.toString() + ".yml");
 	}
-
+	
 	public File getUserFileFromString(final String name)
 	{
 		final File userFolder = new File(ess.getDataFolder(), "userdata");