Help!

Not sure if this will change anything, but you might want to create a class that implements CommandExecutor and try registering your command through that class and not just your main class.

 

You can use a separate class:

Code (Text):

public class Commands implements CommandExecutor {

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if(!(sender instanceof Player)){ //Is a player or console
            return true;
        }
        if(cmd.getName().equalsIgnoreCase("tester")) { //Command
            Player p = (Player)sender;
            p.sendMessage("§6Test Plugin Was Successful!");
            return true;
        }
        return false;
    }
}

And in your main class:

Code (Text):

public class Test extends JavaPlugin {

    public void onEnable() {
        getCommand("tester").setExecutor(new Commands());
    }
}

 

No problem

 

Everything looks ok. Do you have any other plugins that you wrote running on that other server? Because you package naming is bound for problems... (for future reference use all lowercase and have your names me. <yourname>. <pluginname>).
Otherwise there is a chance that the plugin really isnt in the plugin folder xD double check it... we always look past the simple mistakes and they are the hardest to debug