Problem/Bug Selectors (@e , @p , @r and @a) not working

My realms trial expired and me and my friends wanted to continue our work.

We use command blocks heavily (such as /kill @e[type=Skeleton,r=50] ).

However, once we switched to bukkit, thing got out of control.

How do I bring back Selectors in command blocks and commands.

Plugins:
ClearLag , Essentials , EssentialsChat , EssentialsProtect , multiworld , PermissionsEx, Vault , WorldEdit.

 

@TheEnderCrafter9
First, make sure that command blocks are enabled on your server. Go in to your server directory, open the server.properties file, and find this field:

Code:

enable-command-block=false

If this is set to true, then you can ignore this step. If not, replace "false" with "true", and save the file.

Now, I'd recommend you to read this:
http://wiki.bukkit.org/Commands.yml

I see you're using Essentials. This plugin overrides the default kill command, so try using this command instead:

Code:

/minecraft:kill @e[type=Skeleton,r=50]