I get a tonne of errors, including reloading the plugin, vanishing, join, etc.

I dont have Spout installed.

2012-02-20 03:45:41 [SEVERE] Could not pass event org.bukkit.event.player.PlayerJoinEvent to VanishNoPacket
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$103.execute(JavaPluginLoader.java:1026)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:57)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:453)
at net.minecraft.server.ServerConfigurationManager.c(ServerConfigurationManager.java:133)
at net.minecraft.server.NetLoginHandler.b(NetLoginHandler.java:121)
at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:40)
at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:61)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:537)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:435)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader$103.execute(JavaPluginLoader.java:1024)
... 9 more
Caused by: java.lang.NoSuchMethodError: org.bukkit.entity.Player.canSee(Lorg/bukkit/entity/Player;)Z
at org.kitteh.vanish.VanishManager.hideVanished(VanishManager.java:239)
at org.kitteh.vanish.VanishManager.resetSeeing(VanishManager.java:119)
at org.kitteh.vanish.listeners.ListenPlayerJoin.onPlayerJoinEarly(ListenPlayerJoin.java:28)
... 14 more

As the download page states, you need 1.1-R4 to run this plugin

Ah, okay. I put the CraftBukkit-1.1-R4 in the folder, but didn't set the path.. :P that's why