Solved DELETE

Maybe write @Override over the onpacketSending method

Code (Text):

        protManager.addPacketListener(new PacketAdapter(this, ListenerPriority.NORMAL, new PacketType[] { PacketType.Play.Server.TAB_COMPLETE })
        {
            @SuppressWarnings("unused")
            @Override //<---
            public void onpacketSending(PacketEvent e){

                if ((e.getPacketType() == PacketType.Play.Server.TAB_COMPLETE)){
                    if(!e.getPlayer().hasPermission("SomePermission")){

                        e.setCancelled(true);
                    }
                }
            }
        });

 

I'm pretty sure you don't need to check if e.getPacketType() == PacketType.WHATEVER, because you already specified in the PacketAdapter constructor that you wish to listen only to tab complete packets.

That's because the method is onPacketSending, not onpacketSending. Case matters.

 

Have you tried to spell it onPacketSending instead of onpacketSending