Now using Project Ares's unofficial craftbukkit 1.5. I know these errors are technically not supported since the bukkit team hasn't released 1.5 builds yet, but I figured I might as well post these anyways. Sorry to have bothered any devs.

2013-03-13 18:38:04 [SEVERE] Error occurred while enabling VoxelSniper v5.168.5-SNAPSHOT-jnks200 (Is it up to date?)
java.lang.NoClassDefFoundError: net/minecraft/server/v1_4_R1/EntityLiving
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:2413)
at java.lang.Class.getConstructor0(Class.java:2723)
at java.lang.Class.getConstructor(Class.java:1676)
at com.thevoxelbox.voxelsniper.SniperBrushes.getBrush(SniperBrushes.java:240)
at com.thevoxelbox.voxelsniper.SniperBrushes.getSniperBrushes(SniperBrushes.java:180)
at com.thevoxelbox.voxelsniper.MetricsManager.start(MetricsManager.java:138)
at com.thevoxelbox.voxelsniper.VoxelSniper.onEnable(VoxelSniper.java:314)
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:217)
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:457)
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:381)
at org.bukkit.craftbukkit.v1_5pre_R1.CraftServer.loadPlugin(CraftServer.java:256)
at org.bukkit.craftbukkit.v1_5pre_R1.CraftServer.enablePlugins(CraftServer.java:238)
at net.minecraft.server.v1_5pre_R1.MinecraftServer.j(MinecraftServer.java:311)
at net.minecraft.server.v1_5pre_R1.MinecraftServer.e(MinecraftServer.java:290)
at net.minecraft.server.v1_5pre_R1.MinecraftServer.a(MinecraftServer.java:247)
at net.minecraft.server.v1_5pre_R1.DedicatedServer.init(DedicatedServer.java:151)
at net.minecraft.server.v1_5pre_R1.MinecraftServer.run(MinecraftServer.java:389)
at net.minecraft.server.v1_5pre_R1.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_4_R1.EntityLiving
at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:70)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
... 19 more

The errors appear because sniper is not compatible with any Bukkit version except 1.4.x ....and this is because the Bukkit team decided to do some ridiculous renaming. We cannot update sniper to 1.5 as long as there is no 1.5 development build of Bukkit. I'll check later today but I think there is no 1.5 stuff in the repository at the moment.

A 1.5 build wouldn't work with the hack @mibby is using anyway. He's been going around to tons of projects spamming them with these "errors".

Since it is a mod and not official Bukkit I gonna mark this as invalid and close the issue.