Just updated my VoxelSniper to the latest and I get this in console:

04:34:16 [INFO] This server is running CraftBukkit version git-Bukkit-1.2.5-R4.0-b2222jnks (MC: 1.2.5) (Implementing API version 1.2.5-R4.0)
04:34:23 [SEVERE] Could not load 'plugins\VoxelSniper.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError
: com/thevoxelbox/voxelsniper/VoxelSniper : Unsupported major.minor version 51.0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:151)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:213)
at org.bukkit.craftbukkit.CraftServer.(CraftServer.java:189)
at net.minecraft.server.ServerConfigurationManager.(ServerConfigur
ationManager.java:53)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:166)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.UnsupportedClassVersionError: com/thevoxelbox/voxelsniper/V
oxelSniper : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$000(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:41)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:29)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:140)
... 8 more
04:34:23 [INFO] [VoxelUpdate] Loading VoxelUpdate v1.1.4

I tried looking for a download link for the previous version so I could downgrade back to that working version, but I came up with nothing because of VoxelUpdate.

Help would be much appreciated.

Now being a java dev and former mod maker this error is from when a file is compiled with a new version of java ie. 7 and it is trying to be ran by an older version ie. 6

For users on macs (like me) we don't have access to java 7 yet. In addition some people may not want to upgrade as of the moment.

09:11:15 [SEVERE] Could not load 'plugins/VoxelSniper.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError: com/thevoxelbox/voxelsniper/VoxelSniper : Unsupported major.minor version 51.0
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:150)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:305)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:230)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:213)
at org.bukkit.craftbukkit.CraftServer.(CraftServer.java:189)
at net.minecraft.server.ServerConfigurationManager.(ServerConfigurationManager.java:53)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:157)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:423)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.UnsupportedClassVersionError: com/thevoxelbox/voxelsniper/VoxelSniper : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:41)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:29)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:139)
... 8 more
Same thing as above... Why can't we downgrade?

awh so all it needs is my servers java upgraded from 6 to 7? thanks skeletonofchaos :) Wonder what can voxel do for other people? (i.e mac users...) aint really that fair :P

Just found a dev build of java 7 for mac that works so I think this can be closed.

Sorry guys. Someone of our team messed up and build the jar incorrectly.
There should be a new Version available and it's going to work again as you would expect.

Sorry for the inconvenience. Have fun playing with Sniper again.