From the server log:
2013-01-04 13:19:45 [INFO] McYorlik issued server command: /vr -1
2013-01-04 13:19:45 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'vr' in plugin VoxelSniper v5.168.3-SNAPSHOT-jnks187
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46)

Should be catched
Cheers
Yorlik

That's not enough log text for us to figure out a) what went wrong and b)
where things went wrong. Post the complete exception stack trace, please.

I think it was just the wrong input "-1" i made .....
Here is the full stack trace:

2013-01-04 13:17:24 [INFO] McYorlik issued server command: /vi
2013-01-04 13:17:37 [INFO] McYorlik issued server command: /b b ii
2013-01-04 13:17:46 [INFO] McYorlik issued server command: /vi
2013-01-04 13:17:50 [INFO] McYorlik issued server command: /vr
2013-01-04 13:18:04 [INFO] McYorlik issued server command: /vri
2013-01-04 13:18:15 [INFO] McYorlik issued server command: /vir
2013-01-04 13:18:30 [INFO] McYorlik issued server command: /vir
2013-01-04 13:18:46 [INFO] McYorlik issued server command: /vir
2013-01-04 13:18:55 [INFO] McYorlik issued server command: /vir 0
2013-01-04 13:19:12 [INFO] McYorlik issued server command: /vs default
2013-01-04 13:19:18 [INFO] McYorlik issued server command: /b b ii
2013-01-04 13:19:29 [INFO] McYorlik issued server command: /vi
2013-01-04 13:19:38 [INFO] McYorlik issued server command: /b b ii
2013-01-04 13:19:45 [INFO] McYorlik issued server command: /vr -1
2013-01-04 13:19:45 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'vr' in plugin VoxelSniper v5.168.3-SNAPSHOT-jnks187
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46)
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:186)
at org.bukkit.craftbukkit.v1_4_6.CraftServer.dispatchCommand(CraftServer.java:514)
at net.minecraft.server.v1_4_6.PlayerConnection.handleCommand(PlayerConnection.java:979)
at net.minecraft.server.v1_4_6.PlayerConnection.chat(PlayerConnection.java:897)
at net.minecraft.server.v1_4_6.PlayerConnection.a(PlayerConnection.java:852)
at net.minecraft.server.v1_4_6.Packet3Chat.handle(Packet3Chat.java:44)
at net.minecraft.server.v1_4_6.NetworkManager.b(NetworkManager.java:290)
at net.minecraft.server.v1_4_6.PlayerConnection.d(PlayerConnection.java:112)
at net.minecraft.server.v1_4_6.ServerConnection.b(SourceFile:39)
at net.minecraft.server.v1_4_6.DedicatedServerConnection.b(SourceFile:30)
at net.minecraft.server.v1_4_6.MinecraftServer.r(MinecraftServer.java:598)
at net.minecraft.server.v1_4_6.DedicatedServer.r(DedicatedServer.java:224)
at net.minecraft.server.v1_4_6.MinecraftServer.q(MinecraftServer.java:494)
at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
Caused by: java.lang.ArrayIndexOutOfBoundsException: -1
at org.bukkit.Material.getMaterial(Material.java:532)
at org.bukkit.Material.matchMaterial(Material.java:564)
at com.thevoxelbox.voxelsniper.VoxelSniperListener.commandSniperVr(VoxelSniperListener.java:518)
at com.thevoxelbox.voxelsniper.VoxelSniperListener.onCommand(VoxelSniperListener.java:58)
at com.thevoxelbox.voxelsniper.VoxelSniper.onCommand(VoxelSniper.java:234)
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
... 15 more
2013-01-04 13:19:52 [INFO] McYorlik issued server command: /vr 15
2013-01-04 13:20:02 [INFO] McYorlik issued server command: /vr
2013-01-04 13:20:06 [INFO] McYorlik issued server command: /vir 0

ADDENDUM: VS totally rocks ! I LOVE it !

I just looked it up. It seems that the method bukkit provides for retrieving Materials over IDs is flawed in it's design and doesn't fit it's functionality contract. I might submit a patch for that.

Ok Bukkit/Bukkit#751 got merged. Should be fixed in next build.