Something

Index: L2J_GameServer/src/main/java/net/sf/l2j/gameserver/model/actor/instance/L2ClassMasterInstance.java
===================================================================
--- L2J_GameServer/src/main/java/net/sf/l2j/gameserver/model/actor/instance/L2ClassMasterInstance.java	(revision *****)
+++ L2J_GameServer/src/main/java/net/sf/l2j/gameserver/model/actor/instance/L2ClassMasterInstance.java	(working copy)
@@ -241,7 +241,12 @@
         if (_log.isDebugEnabled()) _log.debug("Changing class to ClassId:" + val);
         player.setClassId(val);
         
-        if (player.isSubClassActive()) player.getSubClasses().get(player.getClassIndex()).setClassId(
+        if (player.isSubClassActive() && (player._inEventCTF || player._inEventDM || player._inEventTvT || player._inEventVIP)){
+            player.sendMessage("You can't change subclass while in events.");
+            return;
+        }
+        
+        else if (player.isSubClassActive()) player.getSubClasses().get(player.getClassIndex()).setClassId(
                                                                                                      player.getActiveClass());
         else player.setBaseClass(player.getActiveClass());