Bukkit

What steps will reproduce the problem?
1. Enable flag "deny-spawn"
2. Run command "/ps flag deny-spawn zombie"
3.

What is the expected output? What do you see instead?
Expected result: deny spawning of zombies, but can still spawn friendly mobs such as chickens.

Instead, the following happens:

In-game: An internal error has occurred.

Console:
org.bukkit.command.CommandException: Unhandled exception executing command 'ps' in plugin ProtectionStones v1.8f
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:168)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:492)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:878)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:825)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:807)
        at net.minecraft.server.Packet3Chat.handle(Packet3Chat.java:44)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:281)
        at net.minecraft.server.NetServerHandler.d(NetServerHandler.java:109)
        at net.minecraft.server.ServerConnection.b(SourceFile:35)
        at net.minecraft.server.DedicatedServerConnection.b(SourceFile:30)
        at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:583)
        at net.minecraft.server.DedicatedServer.q(DedicatedServer.java:212)
        at net.minecraft.server.MinecraftServer.p(MinecraftServer.java:476)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:408)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Enum
        at com.sk89q.worldguard.protection.flags.EnumFlag.marshal(EnumFlag.java:29)
        at com.sk89q.worldguard.protection.flags.SetFlag.marshal(SetFlag.java:85)
        at com.sk89q.worldguard.protection.flags.SetFlag.marshal(SetFlag.java:36)
        at com.sk89q.worldguard.protection.databases.YAMLDatabase.addMarshalledFlag(YAMLDatabase.java:280)
        at com.sk89q.worldguard.protection.databases.YAMLDatabase.getFlagData(YAMLDatabase.java:268)
        at com.sk89q.worldguard.protection.databases.YAMLDatabase.save(YAMLDatabase.java:240)
        at com.sk89q.worldguard.protection.databases.AbstractProtectionDatabase.save(AbstractProtectionDatabase.java:43)
        at com.sk89q.worldguard.protection.managers.RegionManager.save(RegionManager.java:69)
        at com.axeldios.ProtectionStones.ProtectionStones.onCommand(ProtectionStones.java:943)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 15 more

What version of the product are you using?
Latest.

Do you have an error log of what happened?
See above.

Please provide any additional information below.

At this time that flag is not supported, as you know WorldGuard has lots of flags and they are being changed and updated to add more features.

This maybe supported in the next version of PS but there are no guarantees it will be.