Coding Bukkit Plugin Help

So i have been trying to make my own plugin recently on my mac computer and i keep having a error pop up in game that says

* An internal error occurred while attempting to perform this command *

I have tried everything i have uninstalled java and reinstalled it, i made a new bukkit server to test it on, i have went over the code multiple times and it all is correct but i can seem to find the problem if someone can help me fix this problem.

Here is a picture of the command in game-

 

I think it would help if you included some of the actual code you wrote so that others could go over it. :)

 

Maybe is Minecraft Versions fault... Look what version is your server and for what version is your plugin...

 

It means your command has caused an exception.
If you still need help, copy-paste the log of your console and the code of the command class here and gimme the url.