I'm trying to add new variables into player accounts (for slayer tasks) and whenever I try to load old accounts (ones created before I added the code) it gives me this error. But if I create a new account it loads just fine.
If anyone can help me fix this error I would much appreciate it.

[SerializableFilesManager] Recovering account: cole
ERROR! THREAD NAME: New I/O server worker #1-1
java.lang.ClassCastException: cannot assign instance of com.rs.game.player.conte
nt.slayer.SlayerTask to field com.rs.game.player.Player.slayerTask of type com.r
s.game.player.actions.slayer.SlayerTask in instance of com.rs.game.player.Player

at java.io.ObjectStreamClass$FieldReflector.setObjFie ldValues(Unknown So
urce)
at java.io.ObjectStreamClass.setObjFieldValues(Unknow n Source)
at java.io.ObjectInputStream.defaultReadFields(Unknow n Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unkno wn Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at com.rs.utils.SerializableFilesManager.loadSerializ edFile(Serializable
FilesManager.java:67)
at com.rs.utils.SerializableFilesManager.loadPlayer(S erializableFilesMan
ager.java:32)
at com.rs.net.decoders.LoginPacketsDecoder.decodeWorl dLogin(LoginPackets
Decoder.java:167)
at com.rs.net.decoders.LoginPacketsDecoder.decode(Log inPacketsDecoder.ja
va:41)
at com.rs.net.ServerChannelHandler.messageReceived(Se rverChannelHandler.
java:98)
at org.jboss.netty.channel.SimpleChannelHandler.handl eUpstream(SimpleCha
nnelHandler.java:100)
at org.jboss.netty.channel.DefaultChannelPipeline.sen dUpstream(DefaultCh
annelPipeline.java:564)
at org.jboss.netty.channel.DefaultChannelPipeline.sen dUpstream(DefaultCh
annelPipeline.java:559)
at org.jboss.netty.channel.Channels.fireMessageReceiv ed(Channels.java:27
4)
at org.jboss.netty.channel.Channels.fireMessageReceiv ed(Channels.java:26
1)
at org.jboss.netty.channel.socket.nio.NioWorker.read( NioWorker.java:351)

at org.jboss.netty.channel.socket.nio.NioWorker.proce ssSelectedKeys(NioW
orker.java:282)
at org.jboss.netty.channel.socket.nio.NioWorker.run(N ioWorker.java:202)
at org.jboss.netty.util.ThreadRenamingRunnable.run(Th readRenamingRunnabl
e.java:108)
at org.jboss.netty.util.internal.DeadLockProofWorker$ 1.run(DeadLockProof
Worker.java:44)
at java.util.concurrent.ThreadPoolExecutor.runWorker( Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (Unknown Source)
at java.lang.Thread.run(Unknown Source)