Bukkit

What steps will reproduce the problem?
1. Install VoxelUpdate, as given at http://www.voxelwiki.com/minecraft/VoxelUpdate
2. (With my account, which is added in the admns.txt) use /voxelinstall VoxelSniper (doing the same with others did come out with the same error)

What is the expected output? What do you see instead?
I expect VoxelSniper, or any other plugin, to be installed and activated. Instead, I get an internal server error, and the console shows up with the error log below. After that, using /voxelplugins reveals that the state of the plugins I tried to install is now "Disabled". Yet, the plugins are downloaded into my plugins folder, but not enabled, this needs a restart to be done.

What version of the product are you using?
VoxelUpdate 1.0.13
CB 1597, current RB

Do you have an error log of what happened?
org.bukkit.command.CommandException: Unhandled exception executing command 'voxelinstall' in plugin VoxelUpdate v1.0.13
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:165)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:378)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:757)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:722)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:715)
        at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:180)
        at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:33)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:93)
        at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:550)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:527)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)
Caused by: java.lang.NullPointerException
        at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:294)
        at com.thevoxelbox.voxelupdate.UpdateManager.doDownload(UpdateManager.java:160)
        at com.thevoxelbox.voxelupdate.VoxelUpdate.onCommand(VoxelUpdate.java:134)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 14 more

Please provide any additional information below.
My plugins folder has the user I'm running the server under as owner. The downloaded files have (in chmod terms) 644 rights. I suggest that thus it has at least nothing to do with missing file permissions ;D

I get this as well, it still seemed to have installed the plugin however, I have auto-update on which is suppose to enable the plugin immediately which I assume is where the error is at because it shows up as disabled. It should enable when the server restarts I'll let you know if it does when that happens.

I see this line in your output:

at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:180)

I take it you are using Spout? We do not support Spout, since the VoxelBox runs Bukkit.