Bukkit

When I use the /rankup command it says "An internal error has occured"
I am using Vault, I have reinstalled the plugin many times.
I am using PermissionsEX

It showed this in the command prompt:

[11:48:47] [Server thread/INFO]: Vikram987 issued server command: /rankup
[11:48:47] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'rankup' in plugin Rankup v1.2
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:196) ~[minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at org.bukkit.craftbukkit.v1_7_R1.CraftServer.dispatchCommand(CraftServer.java:542) ~[minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.PlayerConnection.handleCommand(PlayerConnection.java:932) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.PlayerConnection.a(PlayerConnection.java:814) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.PacketPlayInChat.a(PacketPlayInChat.java:28) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.PacketPlayInChat.handle(PacketPlayInChat.java:47) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.NetworkManager.a(NetworkManager.java:146) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.ServerConnection.c(SourceFile:134) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:655) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.DedicatedServer.u(DedicatedServer.java:250) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.MinecraftServer.t(MinecraftServer.java:545) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:457) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
Caused by: ru.tehkode.permissions.exceptions.PermissionsNotAvailable: Permissions manager is not accessable. Is the PermissionsEx plugin enabled?
    at ru.tehkode.permissions.bukkit.PermissionsEx.getPermissionManager(PermissionsEx.java:203) ~[?:?]
    at net.milkbowl.vault.permission.plugins.Permission_PermissionsEx.getGroups(Permission_PermissionsEx.java:270) ~[?:?]
    at com.fvza.rankup.Ranking.rankup(Ranking.java:35) ~[?:?]
    at com.fvza.rankup.bukkit.Commands.onCommand(Commands.java:32) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[minecraft_server.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
    ... 13 more